Our KitchenAid mixer has two controls: one for speed and one to lock the head pivot. The speed knob is still there:
The pivot lock knob broke off some time ago, leaving just a metal stem.
Today I modeled something like the speed control knob to install on the pivot lock. Heated up the metal arm with a butane torch for just long enough to press the knob all the way on and then cool in place; it’s probably not coming off any time soon.
I might sand it, or I might just leave it be. I could have printed it in black to match, but somehow the gray filament was calling my name, so I used that instead.
If anyone else ever needs such a thing, the model is available.