To reset the service airbag light on your GMC Terrain, follow these simple steps: 1. Sit in the driver's seat and make sure the ignition is turned off. 2. Locate the OBD-II port under the dashboard on the driver's side. 3. Connect an OBD-II scanner to the port and turn on the ignition. 4. Use the scanner to clear any trouble codes related to the airbag system. 5. Once the codes have been cleared, turn off the ignition and disconnect the scanner. 6. Restart the vehicle and the service airbag light should be reset.