WARNING: This page is about a different car, the 2002 Pontiac Montana, 2002 Oldsmobile Silhouette, and 2002 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
Open the sliding door.
Loosen 2 screws on the rear door striker.
Move the striker in and out in order to adjust the rear edge of the sliding door, as needed.