Promote pawn to king
The rules don't say they can promote to any piece.
https://handbook.fide.com/chapter/E012023
3.7.3.3 When a player, having the move, plays a pawn to the rank furthest from its starting position, he/she must exchange that pawn as part of the same move for a new queen, rook, bishop or knight of the same colour on the intended square of arrival. This is called the square of ‘promotion’.