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.
Remove the catalytic converter front heat shield nut (1).
Remove the 4 catalytic converter front heat shield bolts (2).
Remove the catalytic converter front heat shield (3).