If you have the six digit order number, you can go to GMC.com. Look for the little box on the right that says "Message Us." Click on it, follow the prompts until you see the option of Check My Vehicle Order. It will then ask if you are in the United States, hit enter again without answering this question and it will transfer your chat to a live person. Otherwise, it is automated and not very informative.
If you do not have the order number, ask your salesman or the General Manager of the dealership for it.