How can I change the subtitles H6 in icongrid

A child-theme solution could be to have an own icongrid.php in your child-themes/shortcodes folder.
This folder had to be created by yourself. Put in a copy of the icongrid.php ( from : enfold/config-templatebuilder/avia-shortcodes/icongrid/ )
edit that file arround line 1884

$subtitle_el = 'h6';

and change that to

$subtitle_el = 'p';

this snippet is for using the child-theme alternative files and comes to child-theme functions.php:

function avia_include_shortcode_template($paths){
  $template_url = get_stylesheet_directory();
      array_unshift($paths, $template_url.'/shortcodes/');
  return $paths;
}
add_filter('avia_load_shortcodes', 'avia_include_shortcode_template', 15, 1);

see docu: Link