On the server, go to Saves/world name/seed name/players. In the are eos files, 3 for each. Your eos number is assigned & noted in the servers output log for each player. The server admin needs to delete the 3 files associated with your eos. The server does not need to be stopped to do this so it can be done on the fly. When you join next, you will be starting over at level 1. The server admin can give you your inventory back using the creative menu and can give your levels back using the givexp command(I think that’s the correct command, someone correct me if I’m wrong).