How do you lower the sapre tire on a 2003 Chevy Trailblazer

It should be held in the center but a very large bolt that is attached to the under carriage. Also your owners manual will tell you exactly how to remove it.

if I had a manual I wouldnt be looking here

You have to crank it up as tight as you can to release the safety catch and then crank the tire down. Only drawback is that the safety catches are known to seize up and then you have to cut the tire out of the bracket (cut the bracket, not the tire ... obviously). Once it is cut out, then you have to replace the bracket or just keep the spare tire inside the back end of the vehicle.