Air vent stuck in closed position

I have a 2007 Kia Rondo and the air vent on the passenger side is stuck in the “off” position. My mechanic said they’d charge me $45 to diagnose it which I don’t want to do. It seems like it should be an easy fix, but I’m not sure how to access the inside of the vent. Through the glove box? Any ideas would be appreciated!