can you temporarily remove the child-theme tag.php – and put this to your child-theme functions.php:

add_filter('avf_blog_style','avia_change_tag_blog_layout', 10, 2); 
function avia_change_tag_blog_layout($layout, $context){
if($context == 'tag') $layout = 'blog-grid';
return $layout;
}

add_filter('avf_post_slider_args', function($atts, $context){
  if($context == 'tag') {
    $atts['type']  = 'grid'; 
    $atts['columns']  = 1;
  }
  return $atts;
}, 10, 2);

and this to quick css

#top.tag .entry-content-wrapper .post-title{
  margin-bottom: 40px
}

#top.tag .slide-entry-wrap {
  margin-bottom: 10px;
}

#top.tag .slide-image {
  display: none !important;
}

#top.tag .slide-content > :not(.entry-content-header) {
  display: none;
}

#top.tag .slide-entry-wrap .entry-content-header .slide-entry-title:before {
  content: "Article:";
  font-size: inherit;
  font-weight: inherit;
  color: #666;
  padding-right: 15px;
}

you can address these icons via attribute selector.
f.e. here on a testpage – see the first iconbox on the left: https://webers-testseite.de/
Open the alb ( in this case the iconbox – and hover the wanted icon to inspect the code behind that font-icon – here it is: ue837
get rid of the u ( i guess it stands for unicode ) and note your code for the icon as : \e837 ( the backslash is used here )
click to enlarge the image:

now my replacement code on quick css is:

div[data-av_icon="\e837"] {
	content: " ";
	background-image: url(/wp-content/uploads/ezgif-4-64b6614e32.gif);
	background-size: contain;
	background-repeat: no-repeat;
       font-size: 0 !important
}

this gif will now replace all occurrences of this font icon. And if the replacement image is transparent the alb settings for border-color and background-color will be adjustable too. ( Font-color : NOT ; self-evident )
:LOL and even in the preview it will be replace:

BUT: i see that some of those icons are placed in a different way ( f.e. as span – so be carefull to adjust the code then !

put it in General Styling – Quick CSS
maybe an important is necessary :

#top .image-overlay .image-overlay-inside::before {
  content: "\e80f" !important;
  font-size: 50px;
  color: #fff !important;
}

#top div .avia-gallery .avia-gallery-big {
  padding: 0px !important;
  border-style: none !important;
}

#top div .avia-gallery img {
  border-style: none !important;
  padding: 0px !important; 
}

the : content: "\e80f" is a little camera – if you like to show a real image – code has to be adjusted.
if you like to have it specific only for one gallery – give a custom-class to that gallery – and this has to be part of the css code.

PS: i do not see your private content area – i’m participant as you- so i only could investigate own or the enfold demo pages to give advice.

use on that the quick css input field.

if you mean this “Gallery with Preview” on https://kriesi.at/themes/enfold/shortcodes/gallery/
try:

#top .image-overlay .image-overlay-inside::before {
  content: "\e80f" !important;
  font-size: 50px;
  color: #fff !important;
}

#top div .avia-gallery .avia-gallery-big {
  padding: 0px;
  border-style: none;
}

#top div .avia-gallery img {
  border-style: none;
  /*** padding: 0px; *** - if you like ***/
}

seems like when i use below css i can see the green button but not the other button.

@media only screen and (max-width: 767px) {
.html_header_transparency #top .avia-builder-el-0 .slideshow_caption {
padding-top: 10px;
}

#top #wrap_all .avia-slideshow .av-slideshow-caption {
font-size: 30px;
}

#top .avia-slideshow .av-slideshow-caption p {
font-size: 14px;
}
#top .flex_column_table.av-equal-height-column-flextable.av-9y4su-ed9cb8f9ef6e3819ca120920f518c18b {
margin-top: -115px;
}
}
@media only screen and (max-width: 767px) {
.av-slideshow-caption .container {
width: 95%;
max-width: 95%;
}
}

#top .av_header_transparency {
background: rgba(0, 0, 0, 0.4);
}
.home #av_section_1 .iconbox_content {
min-height: 591px;
}

#avia2-menu {
position: relative;
top: -3px;
}

#top .flag-dansk {
background: url(‘https://www.zorbas.dk/wp-content/uploads/2017/03/dansk-flag.png’) center center no-repeat !important;
height: 18px;
width: 50px;
text-indent: -9999em;
}

#top .flag-svensk {
background: url(‘https://www.zorbas.dk/wp-content/uploads/2017/03/svensk-flag.png’) center center no-repeat !important;
height: 18px;
width: 50px;
text-indent: -9999em;
}

#top .flag-dansk a,
#top .flag-svensk a {
display: block;
}

.custom-tag {
padding: 5px;
background-color: rgba(0,0,0,0.5);
}

#top .widget_nav_menu {
padding-top: 0;
}

.sidebar_left {
-moz-box-shadow: inset -8px 0 20px -10px rgba(0, 0, 0, 0.2);
-webkit-box-shadow: inset -8px 0 20px -10px rgba(0, 0, 0, 0.2);
box-shadow: inset -8px 0 20px -10px rgba(0, 0, 0, 0.2);
}

.sidebar_left .inner_sidebar {
margin-right: 0 !important;
}

.sidebar_left .widget_nav_menu ul li a {
border: 1px solid #e1e1e1;
border-right: 0;
border-left: 0;
color: #666;
margin: 0 0 -1px;
padding: 12px 16px !important;
text-align: left;
}

.sidebar_left .widget_nav_menu ul li.current-menu-item a {
color: #719430;
}

/*8bba34*/

.sidebar_left .widget_nav_menu ul li:first-child a {
border-top: 0;
}

.page-id-2584 #element_avia_17_1 {
width: 100%;
margin-left: 0;
}

.av-catalogue-content {
padding-right: 0px;
}
.avia-testimonial-image {
float: none;
margin: 0 auto 0px auto;
}
.avia-testimonial-meta {
margin-left: 0;
text-align: center;
}

.lch-progrees-bar {
padding-right: 0px;
margin-right: -0px;
}

.page-id-118 .sidebar_left #nav_menu-2 {
display: none;
}

.page-id-120 .sidebar_left #nav_menu-2 {
display: none;
}

.page-id-123 .sidebar_left #nav_menu-2 {
display: none;
}

.page-id-125 .sidebar_left #nav_menu-2 {
display: none;
}

/*
@media only screen and (max-width: 767px) {
.responsive .avia-grid-testimonials .avia-testimonial-meta {
margin-left: 130px;
}}*/

@media only screen and (max-width: 989px) and (min-width: 768px) {
.lch-progress-bar {
padding-right: 0px;
margin-right: 50px;
}
}

@media only screen and (min-width: 768px) {
.home #av_section_2 .entry-content-wrapper {
display: -webkit-flex;
display: flex;
flex-direction: row;
}

.home #av_section_2 .entry-content-wrapper .iconbox,
.home #av_section_2 .entry-content-wrapper .iconbox_content {
height: 100%;
}

.home #av_section_2 .entry-content-wrapper .iconbox_content {
padding-bottom: 0;
}
}

.home #av_section_2 .entry-content-wrapper .iconbox_content {
padding-bottom: 30px!important;
}

.home #av_section_2 .entry-content-wrapper .iconbox_content .avia-button-center {
position: absolute;
bottom: 0;
transform: translateX(-50%);
left: 50%;
width:90%;
}

@media only screen and (max-width: 767px) {
.av-catalogue-price {
font-size: 14px;
position: relative;
}
.av-catalogue-title {
font-size: 14px;
line-height: 1.5em;
}

.avia_textblock {
line-height: 37px;
}

h1 {
line-height: 60px;
}

.fb-page.fb_iframe_widget,
.fb-page.fb_iframe_widget span {
position: static !important;
width: 100% !important;
}

.av-catalogue-content p:last-child {
font-size: 11px;
}

.av-catalogue-image {
float: none;
margin-left: auto;
margin-right: auto;
display: block;
}

.responsive .tabcontainer .tab_content {
padding: 0 5px;
}

.av-catalogue-content p {
font-size: 10px !important;
}

.progressbar-title {
font-size: 11px;
}

.avia_message_box_content {
margin-left: -8px;
margin-right: -8px;
}
}
@media only screen and (max-width: 767px) {
.av-catalogue-price {
font-size: 11px;
position: relative;
}
.av-catalogue-title {
font-size: 11px;
line-height: 1.5em;
}

}
#advanced_menu_toggle, #advanced_menu_hide {
display:block !important;
}
}

/*caldera*/
.caldera-grid {
font-size: 20px;
}

#fld_4934012Caption {
font-size: 12px;
color: green;

}

@media only screen and (max-width: 1024px) {
nav.main_menu, #menu-item-search {
display: block !important;
}
.menu-item {
display: none;
}
.av-burger-menu-main.menu-item-avia-special {
display: block;
}
}

.main_color table caption, .main_color tr:nth-child(even), .main_color .pricing-table>li:nth-child(even), #top .main_color .avia-data-table.avia_pricing_minimal td {
color: #000;
}

#top .av_header_stretch .container {
width: 70% !important;
margin: 0 20px;
}