WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Lower Auxiliary Air Distribution Duct
Courtesy of GENERAL MOTORS CORP.
Remove the left side rear quarter trim panel.
Remove the rear (auxiliary) A/C outlet lower duct bolt (1).