We recently made a video tutorial that may be helpful to you, if you are looking to add boundaries to the map that are not already in CODAP: https://www.youtube.com/watch?v=3VHTb9giboE

Also, if you can’t find a GeoJSON with the boundaries you want by googling, you can create one yourself for regions you select here: https://support.planet.com/hc/en-us/articles/360016337117-Creating-a-GeoJSON-file