Save file 1: Ancient Save file 2: Modern Save file 3: Demi

1. Start new game and exit to main menu when you reach the flight tutorial
2. Go to save data folder (for me this was C:\Users(username)\AppData\LocalLow\PolyKnight Games\InnerSpace)
3. Zip/duplicate the folder of the save file you just used

Every time you reset, you just need to delete one of the save folders and replace it with your copy. After that, open the save file in InnerSpace (InnerSpace will say "Start new game" even though there is already save data for that save file)

You can also exit to the menu when the "Hello?" text pops up (which skips a load) but InnerSpace will then treat the save file as a save file that was already used and I don't know if that is allowed.