How to assign PlayerRoomIndexing

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Hello, I am using Pun Classic and I want to be able to assign players an index number using Exitgames.utilityscript. What I want to do is call the PlayerRoomIndexing script from my game script and be able to check what each player's index number is and then assign them a slot on my score table. I have my score table all set up and running, I tried using the player.ID system but because players can leave and join, this causes the playercount to overflow. So after some research I found tat playerRoomIndexing would be my best chance. I now know what to use, but I dont know how to use it. How can I call functions from this script and assign each player an index number? Thank you :)