your retaining ring came unscrewed. See the threaded ring on the knob portion? You need to slip that off past the 2 "keys" that are sticking out of the side - spring loaded. Once you get the ring off, you need to use it to attach the latch portion back to the dash. The latch portion goes on the back side, and the ring threads into it from the front. Need to be tight. You'll figure it out (an allen wrench does not fit into the ring - you'll see what I mean when you get it off the knob portion). To get the knob portion back in, you need to take a large straightened paper clip or a long thin finish nail and stick it in the small hole right in the middle of the knob. Push the little "keys" down as you push the paperclip in. It will hold these keys down. Once you have them both retracted, put it back in the latch portion and remove the paperclip. That should lock them back together.
rr (probably need to learn paragraphs)