Need some help making a Character selection screen.

Alright so I am trying to make a local multiplayer game and I need to make a way so players can before starting the game, first of all join the game, then set there specific character then lock in
I need a way so that when we are on the screen and a player presses A before anyone else he fills the player 1 slot than the Second person to press A gets 2nd then on and on until everybody is in
my problem is I don’t know how I am supposed to figure out which controller pressed A. some help would be greatly appreciated

I think get player controller number is used for local multiplayer. Probably check the number after A is pressed and use that info