I actually haven’t done it in A20, but in A19 it was indeed 3 files and you didn’t even need to shut the server down to do this. I think in A20 it should be similar although it is a little tougher. In A19 and before, the players were identified by their Steam id. In A20, they are identified by their EOS id. You need to go look at the server output log and find where that player joined the server and that’s where they are assigned their EOS number. Then go to the current Saves folder and in the Players folder and delete the 3 or so EOS files associated with him. He will start over at level one, however a couple of things remain: any doors/boxes that had passwords are saved as well as how much of the map that he previously uncovered.