WARNING: This page is about a different car, the 2004 Buick Regal and 2004 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Rearview Mirror Lamp Bulb & Socket
Courtesy of GENERAL MOTORS CORP.
Install the bulb to the socket.
Fig 2: Pressing Rearview Mirror Lamp Lens Into Mirror
Courtesy of GENERAL MOTORS CORP.
Align the lamp lens to the rearview mirror. Press the lens into place.