Even though there's only one save slot, you can manually back-up your save files and then start a new one if you want! The save file is named "data.sav" and it's located in C:\Users\(YOUR NAME)\AppData\Local\PocketCrystalLeague.
Simply rename it to something else and you'll be able to play a new game. When you want to go back to it, just name it back to "data.sav".