I have a 1993 Lumina Van that has a flat tire. I don't know how to get the spare tire down from under the car. I don't have anything that looks like a wrench

A shop didnt find anything? You have a suspension problem Lets start at the tires is there any mud or crude that affect the balance of your tire? What about wheel bearing is there side to side movement even with the rear,How about the upper ball joint and lower ball joint . a warp drive axle can cause this . If you are certain of there inspection with the suspension the problem is the torque convertor. If that stays lock up whoa you will be shaking like big time

Look at the bumper around the center of it. There should be a hole (sometimes has a cover).
One of the tools that should be with your jack goes in there. It looks like a long flat screwdriver. Insert it into the hole and turn it. A cable will lower the spare as you crank the tool. There should also be a tool, like maybe the lug wrench, that has a square hole in it. That would be used as the crank handle.
Now is the tube that is located behind the hole in the rear bumper is not there, you're kinda screwed. Something would have to be used to reach the mechanism above ther spare so it can turn it.

2005 Honda Odyssey TOURING models originally came with Michelin PAX run-flats and eliminated the traditional dough-nut spare. If your van no longer has run-flats (look at the tire size) then your van has already been De-PAX'd...count your lucky stars because PAX tires run about 300 a tire plus!!! If you have been De-PAX'd then you will need a donut spare (T135/80D17) this goes into the spare tire space located behind the 3rd row of seats. this Site has everything you will need for the spare http://www.hondapartworld.com/1534_SPARE-SHJ

Lift rear hatch and locate and remove cover on driver side rear corner, jack etc should be behind there. Your spare should be hanging under back of van, ahead of rear bumper. Unfortunately, 9 chances out of 10, the cable and mechanism holding it up there will be rusted and won't work, so don't get too frustrated if it won't come down. A lot of people cut the cable, and lay tire in back. Who knows, you may be lucky, and it will work. Good luck ! Be careful, it's heavy, so if you cut cable, have something up against it like a floor jack or something so it doesn't come down on your head.

where is it located im assuming under the back of the van if so look at the back bumper right on top center for a hole with a square that the tool inside that came with the van will slide in and crank it to lower the tire

you could try negotiating... I have found that talking to them helps.
Spare tires are pretty simple. you jack car up, take old wheel off, put spare on, jack car down..... what with the spare tire are you having dificulty with?

It lowers to the ground with a wrench. Lift up the cover from inside of the car.

With the new 2008 models, the spare tire was moved from the rear of the van to a spot below the front seats. The lug for the tire winch is located under a round cover in the floor just in front of and between the two front seats. If you look under the van, you will see the black tire-shaped cover for the spare.

If you have the standard tires on the van the spare is located under the van about center. If the van came with "run flat" tires, there is no spare.

lift the rug at edge of the floor right above the bumper there is a big nut turn counter clockwise