Find your jack kit, there should be 2 extension rods with square ends on them. You'll find a small pop off plate on the bumper, assemble the extension rods and stick them in the opening (you can look from underneath to see where the rod needs to hit). Once you're locked on use the supplied tool to turn the rods...this lowers or raises the spare tire.
This is common on most GM trucks/SUVS from 06 and up. My concern would be why it's loose. If you've never used the spare the system should have remained in it's factory position. It's possible your truck slipped through a lazy GM employee who did not ensure the spare tire winch system was at spec. If you secure the tire and it loosens again in the near future chances are the little winch is no good. I'd imagine you're still under warranty, if this occurs take it in and have it replaced.
Hope this helps!