Flipbook - Resizing pages

First time trying out this flipbook thing. The options are a tad bit confusing. I tried watching a how-to video but the icon it says to resize an individual page isn’t where it shows. And the other option to resize all pages is a pay for feature.

I somehow enlarged all my pages and I have no idea how to shrink it back down to the original size. Could someone explain how to do that please for the free version? Thanks!

You can go to Settings Panel at the top right (without select anything) to change the Paper size for individual page.