Instructions
Turn on the PS3. The XMB™ menu will appear.
Turn on the controller that you wish to assign by pressing the PlayStation button in the middle of the controller.
Navigate left to the "Settings" menu. Press "X." Scroll down to the "Accessory Settings" option. Press "X."
Scroll to the "Reassign Controllers" option. Press "X." Scroll through the controller position numbers and select the number that you would like to assign the controller to. Press "O" to finish and go back to the XMB menu.