WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Use a flat-bladed tool in order to release the 3 sill plate retaining tabs.
Remove the sill plate from the door frame.
Remove any retaining tabs that remain attached to the door frame.
Fig 1: Rear Door Sill Plate From Door Frame (TrailBlazer EXT & Envoy XL)