This what Carey suggests:
There is a little rocker switch inside of that turn signal unit that switches it from high beams to low beams.
The most common cause of this is the stalk physically hitting the steering wheel hub. Sop, just watch it as you pull and see if that is the case.
If not, then sometimes they just build up gunk and stick. You can try cleaning it out with a dielectric spray grease and compressed air.
I find it easier to work on with the steering wheel out of the way.
Once you pull the wheel (after you make sure the lever isn’t simply hitting the hub) you can also check the 5 small flat head screws to make sure they haven;t backed off enough to allow the metal face of the assembly flex outward and to allow the arm to move the rocker switch enough.