Whenever you upload your .docx into Atticus, it is treated as a new book. If you want to make changes to an existing manuscript, it is best to do those changes in Atticus.
If you’ve made revisions to a few chapters and only want to import those, you can add them in as a new chapter. This feature is helpful if you’re only wanting to import a few chapters; it is not meant to import changes to the entire manuscript.
If you want to learn how to import individual chapters, you can read about that here: Can I import chapters into an existing book?
We hope that helps!