How do I change a word or a name everywhere in my book at once?

From version 1.9.23, open the book's page and press "Replace", next to Codex above the chapter list. Type what to find and what to replace it with. "Whole words only" (on by default) means "Tom" is not found inside "Tomorrow"; "Match case" makes upper and lower case count. Before anything changes, BookyAI lists every place the word is found, with how many times and a short sample of the text around it. Press "Replace" with the number of matches to change them all. Each chapter's old text is kept in its Versions panel, and a copy of every file that changed is saved in the book's history folder.