Best suggestion I have seen is to click on the top tab to [Clear Book]. You may need to have used the 'Auto Layout' first.
Then you must click the tab [Create a Saved Book] so that this book, and its photos, can always be re-opened for further editing by a [Double Click] on the Saved Book Collection.
Regards. My System: Lr-Classic 12.3 Photoshop 24.5, ACR 15.3.1, Lightroom 6.3.1, Lr-iOS 8.0.8, Bridge 13.0.3, Windows-11.