WARNING: This page is about a different car, the 2016 GMC Acadia, 2016 Chevrolet Traverse, and 2016 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Front Seat Back Cushion Finish Panel
Courtesy of GENERAL MOTORS COMPANY
Install the rear seat back cushion panel (1) by inserting the lower clips over the seat back frame.
Push the upper two clips into the seat back frame until the panel is secure.