Remove the h3 tags around Related Posts

Plugins like easy table of content recognize the h3 tags around the title “Related Posts” and hence add this entry to every TOC as in the screenshot

An easy solution would be remove the h3 tags around this title.

For this effect, I have edited and copied to the child-theme folder the files

yarpp-template-example.php

yarpp-template-list.php

yarpp-template-simple.php

Yet this did not help. How can I modify the h3 tags around the Related Posts heading to something else like <b> or <strong> ??