Here's how to rearrange pages in your Monthbook or Monthly Mini in the Chatbooks app:
Tap and hold a photo.
Tap any other photos you want to move.
Tap Move to.
Select the page number you want to move the photos to.
When you're finished, tap Done at the top of the page, next to the chronological sort button (up and down arrows).
Good to know: On iOS, new photos you add are placed in date order.
You can also rearrange pages in your Monthbook or Monthly Mini on Chatbooks.com. Learn how in How do I rearrange pages in a Monthbook, Monthly Mini, or Baby's First Year on the web?
