Turn a post into a teaser

I”ve created several tiny posts in a specific category and used PHP Code to create a list of them on a special page.

The problem: I can’t find any way to have the head or feature image link to an outside site.

Any way to do this? My client isn’t going to be able to handle any code at all.

If you want to see what I mean go to https://www.artleasecanada.ca/links-to-art-organizations/

The idea is the heads and/or images should link to an arts organization, not the post itself.