Shifter loose, slips down and won't go higher than 3rd.

I recently purchased an 86 cabriolet, and it drove fine the first. Day I had it, and then the shifter fell out of place and it took me a long time to ignite out what was wrong.
The shifter seems to have fallen down under the car from what it looks and feels like and a white plastic ring that hold it in place is broken in half. I can lift the shifter up and hold it in place and shift while I drive but it's very difficult and won't ever go into 4th gear.
It's very frustrating. Do I just need to get it put back into place or is there a bigger problem?
Thank you for your time and expertise!