Since this "game" might quickly create quite large save files and you might uninstall this product fairly quickly - you might want to save some disk space since Steam doesn't delete save files when uninstalling this "game"

Open folder where Steam installs your games
Default is
Locate folder "ParkerSpace" and open it (or straight up delete it and ignore step 3 if you uninstalled the game)

Save files are under folder called "Worlds"
In that folder you gonna see other folders with numbers - these are your save files. You can delete them