Enter one of the initials listed below by entering the first two letters, then highlighting (but not entering) the last letter. Then, enter the corresponding code to change and accept the last letter.
At the initial entry screen, enter the first two initials and go to the given spot. Then, hold the given direction to move to the correct third initial (and hold any given buttons) and press 1. This unlocks the player for you to use on the team you pick.