.json part — copy only the UUID itself34ef6c2d-13be-3de0-ba01-6bca1d9af96b).op add <UUID><UUID> with the value you copied. On success you'll see<UUID> is now an operator!.If the player is currently online, you can use their name instead: op add <username>.
op remove <UUID>.json. Player files are stored as <uuid>.json — the file name.json is the UUID.