How do I turn off the high beams on my 1992 Buick?

[qb's Buick]

At my last oil change they wanted to check my high beams. My high-low-beam selector is my turn signal selector. Pulling the selector toward me changes the beam of the headlights.

I was able to switch the lights to high beam, but now the high-low beam selector arm will not work and the lights are stuck on high beam. The dimmer switch is fine, the turn signals are fine, but I can't find a way to change the beam of my headlights back to low-beam.

I don't ever use high beams. I just want have my lights on low beam so I don't feel like an idiot driving after dark.

I have no idea how to get at the dimmer switch, which looks like it's probably inside a hard plastic collar around the steering column. The collar is solid and has no screws or removable parts.

How do I fix this?