1. Confirm whether the account number is correct: log in again and confirm that it is consistent with the previously activated account number, otherwise the activated account book cannot be found under this account number.

2. View the list of activated books: after logging in, you can view the list of activated books and confirm whether the previously activated books are in the list.

3. Multi-way search: You can search for previously activated books by searching, classifying and labeling, such as searching by title, author and ISBN number, or searching by classifying and labeling.

4. Contact customer service: If you can't find the previously activated book by the above methods, you can contact the customer service staff who defend the book, and they will help you solve the problem and retrieve the previously activated book.