GM Service Manual Online
For 1990-2009 cars only

When you are sitting in a comfortable driving position, adjust the mirror so you can see clearly behind your vehicle. Grip the mirror in the center to move it up or down and side to side.

The day/night adjustment allows you to adjust the mirror to avoid glare from any headlamps behind you. Move the adjusting lever toward the driver's side for the day position and toward the passenger's side for the night position. Keep the rearview mirror in the day position when making adjustments to the position of the mirror.