How do I reattach my shifer?

[Number21]

I just bought a '79 C30 with a SM465, my first manual transmission. I've been teaching myself to drive it...imagine my surprise when the shifter just came right out in my hand in the middle of the road.

So I took the boot off and it looks like there's a little collar on top of the ball at the bottom of the shifter that should keep it in, right? How do I get that collar to seat back where it's supposed to be? Obviously it needs to be pushed down and turned, but I can't get it to turn...