Erasing Channels
WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
To erase programmed channels, hold down the 2 outside buttons until the light on the GDO transmitter begins to flash. Individual channels cannot be erased, but can be reprogrammed using the Garage Door Opener Programming and the Training GDO for Rolling Code Receivers procedures.