If you already know which Character you want to use (ie they are in the *Character Panel*), then you just need to put CHARACTER_ just prior to their name (the name listed in the Character Panel). I believe the character needs to be Global as well to be specifically used in Story scripts

Player 1 for example is listed as Player1 in the Character Panel. Scripts often refer to this character by using CHARACTER_Player1. Player 2 is listed as Player2, and is referred to with CHARACTER_Player2.