WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Sunroof Opening Trim Bezel
Courtesy of GENERAL MOTORS CORP.
Position the back of the sunroof opening trim bezel to the headliner.
Press the sunroof opening trim bezel to the headliner until the tabs are fully seated.