Covers are the preview thumbnails you see of your planner in your Notability library.
Swapping in a new design is very simple:
Open up your planner and navigate to yourdashboard page by tapping the Home icon in the top right corner of the planner.
To change the cover design, select the pages icon in the top right corner. The pages panel will appear on the right, giving you the option to preview all of the cover options. Simply press on your favorite design, and drag it to the very top, before Page 1. You’re all set!