Hello, I will do my best to help answer your General Motors Vehicle questions.
Yes it would have been automatic release, after you select a gear from park. Most likely cause is a bad release actuator. There is a manual over ride. It is located directly about the parking brake pedal, and is mot of the time colored yellow, or red, or be bare metal. With the vehicle in park you can manually flip the lever and it will release the park brake.
Its there, but if your not familiar you may have to either feel around or take a closer look.