Files from the applications dir are displayed as books

I recently purchased a PocketBook InkPad 3 Pro. I don't like the default reading app. So I installed KOReader. KOReader is much more my style. However, now the opening screen shows many (50+) new books which aren't new books at all. They're files in the applications/koreader directory.

How do I remove those "books" from the book database (without actually removing them from the applications directory), and I how do I stop the applications directory from being searched for new media?

Thanks!