I imported my own manuscript. Can the AI improve or rewrite my chapters?

Yes, from version 1.9.21, but only when you ask. On the book's page, move the mouse over one of your own chapters and click the wand button. Choose how the AI should work. From your text: "Polish" (smoother sentences and clean grammar, your voice and every sentence that works kept), "In the book's style" (rewritten in the style, tone and reader set for the book), "Expand" (richer scenes and explanations, nothing invented) or "Tighten" (shorter and sharper, nothing that matters lost). Or "Write again from my chapter": BookyAI first writes a plan of your chapter (what happens, in order, and the names, facts and quotes that must stay), then writes the chapter fresh from that plan. Choose "In this book" or "In a copy of this book", tick the box that confirms you want the AI to rewrite your text, and press "Rewrite the chapter". BookyAI never rewrites your own text by itself.