A player in relation to Zoe, consists of a discord account (ID) and one or more League of Legends accounts (Region & Riot ID) that have been "linked" to it.
The connection can be made by administrators with /create player or by yourself (if enabled) with /register.
To add more League of Legend accounts to your player, use the command /add account.
In the config of Zoe you can set whether players who leave the server should be automatically deleted. Alternatively, an adminstrator can do this manually with /delete player.