Unscrew the horizontal attachment nuts at the top of the the inner flap with your fingers. Remove the vertical attachment nuts with the screwdriver. Set the nuts aside in a safe place.
Remove the inner flap piece from the PetSafe door frame. Clean all surfaces on the frame to remove any dirt or grime.
Unscrew the screws on the inner frame of the pet door and remove the inner frame from the door. Remove the outer door flap piece from around the back of the inner pet door frame.
Place the new outer door flap piece in position on the back of the inner pet door frame. Replace the inner pet door frame in the door and screw the screws back in to hold the frame to the door.
Place the inner door flap onto the attachment bolts at the top of the pet door. Replace the attachment nuts on the attachment bolts, loosely. Do not tighten the nuts at this time.
Adjust the inner flap horizontally so it sits evenly against the outer door flap. Tighten the horizontal attachment nuts. Adjust the flap vertically so the magnets at the bottom of the inner and outer flap meet. Tighten the vertical attachment nuts.