How would I go about finding a player even if they're not in the game?

Hello, so I'm making a Developer Panel in Roblox and I want to create a ban function(which I know how to do) but instead of banning a player in the game, how would I make it so you can ban a player from the website(like you type in the name of the player, click ban, and they're banned wether they're in the game or not). Something like how Beat up simulator, where you can type in the name of a player and it finds them from the website, not the game.