Hummer H2 2010 Owner's Manual page 174

To program up to three devices:
1. From inside the vehicle, press the two outside
buttons at the same time for one to two seconds,
and immediately release them.
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2. Locate in the garage, the garage door opener
receiver (motor-head unit). Locate the Learn or
Smart button. It can usually be found where the
hanging antenna wire is attached to the
motor-head unit and may be a colored button.
Press this button. After you press this button, you
will have 30 seconds to complete the following
steps.