How do I edit "About the Author" for one book only?

From version 1.9.17, About the Author is a row in the book's manuscript list, under the back matter. Move the mouse over it and click the pencil. The editor opens with the bio from your author profile; what you change there stays with this book only and is saved as about_author.md in the book's folder. Until you edit it, the row is labelled "from your author profile". To go back to the profile's bio, empty the text in the editor. The photo always comes from the author profile. You can also move the section among the back matter with the arrows under "Include in book". BookyAI never writes this section itself. If your author profile has no bio, you can add one for this book from "Add your own" in the "Front & back matter" card.