These are very delicate and are subject to breakage. You will have to replace it ot have it replaced. I used a screw driver, set it in the right position, and then it go for a few months......until it bothered me. Mine was the passenger side vent.
I just had to buy the vents above the DIC. I bought my car used and both the knobs were busted. I found both vents on ebay but had to take them apart and clean thoroughly, let them dry for a couple of days, reassemble, and they now work as they should.