I created a book and now want a different writing style or tone. Where do I change the voice?

From version 1.9.7, open the book's workspace and find the Voice card in the right panel, under Book details. Choose or type a writing style and a tone (for example "Folksy & Down-to-Earth" and "Warm & Encouraging"), click "Hear this voice" to read a short sample in that voice, then click Save voice. The saved voice applies to everything written from then on: regenerated chapters, chapters added with Extend, appendices and the editor's AI rewrites. Chapters already written keep their text until you regenerate them, one by one with the Regenerate button next to each chapter, or all at once with "Rewrite all chapters in this voice" in the Voice card. Each chapter's previous text stays in its Versions.