RepairPal Certified shops can diagnose and repair your 2013 Buick LaCrosse. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
First thing you need to check is the cabin air filter. Here is a video to show you how to get to yours.
https://www.youtube.com/watch?v=-LhCvrYFn6U
Alex