Once you've added Custom Slides to your book, you may want to change where they're featured. You can move all your slides at once to a new section or to the Front Matter.
Open the section with your custom slides
Select the ones you wish to move
Select 'Move x items to'
Select the section to move them to or create a new section
How do I add or move slides to another book?
Select the slides you wish to move or add to another book
Select the 'Move or add to another book options
Choose the book you want and confirm