Click the "Club Management" tab on the left and click "Players". From your players list, click the name of the player.
Click "Roles" on the left
Click "Edit" on the player role for the organization and not the team. This is critical in order for the ID to show up correctly on the match card.
Select "USYS" in the "Affiliate Name" box, and input the Player ID# in the "ID Number" box. Then click "Save".