First you'll have to customize a button the three buttons that you can customize are the X button the white button and the black button. You can customize these buttons to use force powers or to select a weapon. Now you need to customize the light saber to one of the buttons to do this you need to have the light saber icon selected on the mini menu that comes up on the bottom of the screen and the mini menu must still be on the screen now hold down one of the buttons that can be customized untill you hear a sound.
now just have the light saber on and press the button you used.