Book disappeared from the library

Hi! I bought a new iPhone and I was trying to synchronize it with the old one. I have also an iPad, so I wanted to transfer some documents on it from the old iPhone. I accidentally inactivated the iCloud for “Books”, so all my books disappeared from the iPad (they were saved and downloaded locally). Some of them appeared in the library of my new iPhone, but some notes are missing. Anyway, the books are still present on the iPad when I look for them on the searching tab on the homescreen, but I don’t manage to open the file. I tried to shut it down twice but no change. Any suggestions? Thank you