WARNING: This page is about a different car, the 2005 Buick LaCrosse and 2005 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: 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.