Syncing owned books to iPad from windows

So I have some e-books that I want to send to my older iPad. I have managed this before, some time last year I was able to send these 3 books from my windows computer to my iPhone 11 using iTunes I believe. However now that I'm trying this with my older iPad I can't figure out how to do it. I don't see an option in iTunes anymore to manage my devices, not even my iPhone that previously worked.

I found an app called "Apple Devices" on the windows store that helped update my iPad to 10.3.3, but it doesn't have an option for add books to either device either, just General, music, movies, shows, photos and files, files being apps like Word.

Is there another app to add them too, is there another way to send books between computer and device?

I should note that these books are old and no longer for sale anywhere that I've found outside of pre-owned pocket books.