Instructions
Locate the second player's controller. If you cannot find it, ask the person who was playing on it before.
Locate the PS button on the controller. This is located at the center of most controllers. Hold the PS button down for several seconds until an option appears on the screen asking you if you want to turn the system off. Press X for yes to turn the controller off.
Wait a few moments for the game to detect that the second controller has been turned off. The game will then automatically get rid of the second player.