WARNING: This page is about a different car, the 2019 Buick Cascada, 2018 Buick Cascada, and 2017 Buick Cascada. However, it is still accessible from the selected car via links, so may be relevant.
Open the cooling system. Unscrew the coolant surge tank cap.
For draining the cooling system, open the drain screw (1) on the radiator.