you will have to call a dealer with your codes and have them call the ac delco radio hotline and enter your codes and their dealer number to get the unlock code.
when you get the 4 digit unlock code (write it down somewhere) you use the hour button for the first two digits of the unlock code and the minute button for the last two digits of the unlock code. then when the code is displayed push the am/fm button. SEC should show in the display, then push the power button.