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.
Mark the area of the front side door lower weatherstrip on the vehicle.
Remove the front side door lower weatherstrip (1).
Remove the remaining adhesive material (2) with a suitable tool.