How to make a system where you can switch stages?

So I am making an obby and I have the checkpoints scripted and I realized that whenever I touch a checkpoint I touched before, I spawn there. I realized that I needed a GUI that whenever you click it, it shows each stage you have completed and when you click each stage you have completed, it will teleport you there to that stage. Now to the point. I need to know if there is any function like if the player has touched the part before or if the player's leaderboard stat has been 12 before or something like that. If there is, can you please tell me so that I can implement it onto my game so that everything will be saved? Thank you for your time and thank you in advanced.