How to change header on pages aside from the front page?

Hello,

I started making this website a few years ago, newbie to WordPress, learned a lot from YouTube but then got stuck on a few things and got so frustrated with it that I put the entire project on pause.

I’m revisiting it and although I somehow changed the header on all of the pages different from that of the front page back when I started this project, I now, for the life of me, cannot figure out how to change them again. Coming back to it there were many overdue updates that I did so I’m not sure if that could change anything.

Also, I’ve heard from one individual that some of my pages are showing up where the text is reading as columns, which is not how it is showing on my end. She said it then corrected itself (although I hadn’t changed anything on my end), but I feel like I’ve seen this happen before and may have been one of the reasons I begrudgingly stopped the project some time ago. Any insight? She sent a screenshot if it happening, if there’s somewhere I can upload that for reference. She was viewing on a Mac. I did scroll through some of this support information and saw another user with a similar issue but it said theirs was due to a Background Manager Plugin but I looked and I don’t seem to have that Plugin. Unless, of course, perhaps I did historically and now I somehow do not?

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