WARNING: This page is about a different car, the 2003 Pontiac Montana, 2003 Oldsmobile Silhouette, and 2003 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
Install the sill plate by pushing it into the fastener on the floor
Close the liftgate
Fig 1: Installing Sill Plate To Vehicle Floor (Lift Gate)