Tag archive page: how to replace "posts" with h1 headline and tag description?

sorry, but this is not right; you have marked the description, but what I mean is the word “Posts”:

… and I DO have added a description
(site not yet online):

So could you please tell me in which file (archive.php?) and line I can found this output of the word “Posts”?

I haven’t found this in archive.php, but my PHP is not really good, so perhaps I have overseen it.
(No, I do not want to use just display:none, because I want to edit this text)

Thanks.

Could you please leave this to me, whether I can work something out or not? I just asked you in which file I need to look at, nothing more, the rest is up to me!

Meanwhile I found this out for my own – and it is simple as it could be, if you know the right file:

The word “Posts” on top of the tag archive page is found in tag.php!
Not in archive.php, not in loop-index.php!
Are you sure you know the theme???

I had identified it simply by the h3 tag and a bit of thinking about what file could be responsible for the output of a TAG ARCHIVE, and replaced it with a line:

//	echo "<h3 class='post-title tag-page-post-type-title'>".$label."</h3>";
echo '<div style=" margin-top:20px; margin-bottom:40px;" class="hr hr-custom hr-center hr-icon-yes  "><span class="hr-inner   inner-border-av-border-fat" style=" width:200px; border-color:#f0edee;"><span class="hr-inner-style"></span></span><span class="av-seperator-icon" style="color:#f0edee;" aria-hidden="true" data-av_icon="" data-av_iconfont="entypo-fontello"></span><span class="hr-inner   inner-border-av-border-fat" style=" width:200px; border-color:#f0edee;"><span class="hr-inner-style"></span></span></div>';

The result is:
the tag archive page shows the description, NOT the word “Posts” any more as shown in your demo, and in my case I added the avia line to separate the description from the following posts:

https://www.dropbox.com/s/wg3wnyeahmlrfny/tagphp.jpg?dl=0

This is “too complex” as you said???
To comment out a single h3 line in tag.php????

I do not use a child theme – that does not work, if you modify lots of theme files and some snippets don’t work in child themes at all – but no worry, I have my own “system” to record what files I have modified and what not, so that I can safely update the theme, and it works for me since many years with ENFOLD :-)