Instructions
Find the player who needs to be revived. If you are unsure of the player's position, look for the "Revive" label on your screen and navigate toward it.
Walk up to the injured player until a message appears asking to revive the player. Injured players are confined to crawling, so you might have to look away from your normal line of sight to see them.
Press and hold the "Square" button on your PS3 controller until the player has been fully revived. The process will take less than five seconds, but make sure there are no zombies in the area that can injure you as well.