Next to the executable there is a folder called "stages"

In there there are the game's stages. Feel free to customise them! Here's a template: https://docs.google.com/spreadsheets/d/1FKMxPflcxWOG57fpT2zzLOljm_OAId-Pe5EQZabn...

Make a copy to your google drive (or download it) and you can start creating!