Defrost not working

The short - My defroster is not blowing to the glass. I then observed that I could not force the air away from the dash vents using any of the mode buttons.
I found the actuators under the dash (driver's side) and they appear to be working, at least moving the gears that I could see. II removed the large white gear wheel, and the two levers fell out in pieces. I purchased the levers and attempted to reinstall, but I assume that there is a way to zero or index the gears, and a designated groove for the lever knobs to ride in on the back of the white wheel gear.

There is an inner and an outer groove on the white gear. I am trying very hard to DIY this job but as you know it is a challenge, just in the location of the repair alone. I hope that you can provide guidance on the way this is to be reinstalled and maybe provide insight on a way to do this without laying under the dash, using a small mirror. Or, If I am way off base, a course correction.

Thanks