Depends a lot on the particular radio that you have in the car, base unit or up level with added extra goodies. Below are some basics for you. See if this info helps. Thanks
Push the PWR/VOL knob to turn the radio on.
The volume is adjusted by rotating the PWR/VOL knob.
Speed Compensated Volume (SCV)
Press the AUTO VOL button. The available settings are OFF, LOW, MEDIUM, and HIGH.
Turn the TUNE/DISP knob.
Momentarily press the SEEK/SCAN button.
Hold the SEEK/SCAN button at least 2 seconds.
Six AM, Six FM1 and Six FM2. Six XM1 and Six XM2 if equipped with U2K.
Press and hold desired button until an audible beep is heard.
Steering Wheel Control only
Hold the SEEK/SCAN button at least 4 seconds.
Press and hold the HR or MN button until an audible beep indicates the time set mode has been entered. Once the beep is heard, the time can be set by tapping each button to incrementally adjust the time. Holding down each button will rapidly change the time.
Push the TUNE/DISP knob.
Fade or Balance
Push and release the AUDIO knob until fade or balance appears in the display and adjust by rotating the AUDIO knob.
Bass, Treble or Midrange
Push and release the AUDIO knob until bass, mid, or treb appears in the display and adjust by rotating the AUDIO knob.
Press the AUTO TONE button to cycle through the preset equalization settings.
URGH! Hate to have to say it, but in the whole GM service manual, they do not show a picture of the face plate of the radio. So, I don't know what to tell you. Really makes me feel silly after trying to answer your question with what I thought was an easy answer and and easy fix. I am going to opt out of the question for you, so the other fellows here will know you still need help. I will then send a pm to a couple of guys who nay have something that they can post to show you. Really sorry, be patient and someone will get back to you soon. Thanks
Assuming the radio is factory, Bob is 100% correct on the procedure.
The HR and MN buttons should be on the very bottom left of the radio. They are hard to see because they are not illuminated, below the "Tune DISPL" knob and are the same color as the faceplate. Here is a picture of the radio that is supposed to be in your car. Please confirm this is what you have!
If this helps, please give the accept to Bob!