There is a sqlite database file on your device and the books that you are seeing are coming from that database. If you search this forum you should be able to find the exact query that you need to run against this database to get rid of these books. Don’t forget to backup your data before doing it!
If you are not comfortable with CLI you can use DBeaver Community Edition to browse the database and run queries:
https://dbeaver.io/download/
I don’t think there is any other way to remove these books.