GMC 2008 Yukon Denali Owner's Manual page 150

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.
2-52
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.