How to add a link to header image on a certain area

Dear freinds,
I have a header image on my site, which has an in-built button taht says “ENTER” on that particular area I’d wish to have a link layed behind, so one can jump to another page.
I already have created a child theme. I only need to know where to put a link in the header.ph. and how to delimit it to the area.
Thanks a lot!