2017 platinum reserve heating problem
 

Can someone please tell me how I can stop the cold outside air from coming in on the passenger side floor vent in the winter time. The driver side heater works fine, but the passenger side get cold outside air coming in at the floor level. Had it in the shop a couple of times with no luck. Now I just want to cover or jam shut whatever is letting in the cold air. Any ideas?
Thanks,
bigrc