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.
Connect the electrical connector to the rear seat audio
Install the rear seat audio to the overhead entertainment
Press the rear seat audio until it locks into place.
Fig 1: Connecting Electrical Connector To Rear Seat Audio