Adding images to the sub categories

Dear people

I’m trying to add thumbnails to the sub categorie links that appear when the users opens one of the categories.

I have been able to fiend where the sub categories are called .
themes>DT>search.php line 40: <?php hook_gallerypage_results_before(); ?>
I tryed to add this file to my custom child theme in order to edit it
themes>myChildtheme>search.php
but I found that it affect the search results page only (but the search.php in DT only affects the category page, where the URL sais “listing-category/exampleCategory”)

That confuses me a little which file do I need to add to my child theme in order to edit this page? and is there an easy way to add the thumbnails to those sub categories?

Thank you all in advance