Where to find header.php

Hi,

currently, I’m trying to implement a custom CookieYes GTM template within my website (see support ticket: https://www.ads-software.com/support/topic/make-google-site-kit-gdpr-compliant/#post-17878922)
I’m not able to find the proper header.php for the FotaWP theme. Where can I find it on my fileserver?

Thank you in advance

The page I need help with: [log in to see the link]