How do you adjust the rear brakes on a 1999 Dodge Caravan?

Are the rear disc brakes or rear drum brakes?

If they are disc brakes, ther is no adjustment. If they are drum brakes, you adjust them by backing up and hitting the brakes. Do it in an empty parking lot.

If they are drum style brakes, simply put the van in reverse, and accelerate backwards about 10 feet, and jam on the brakes.. repeat a few times and the auto-adjusters will tension the shoes against the drum properly accounting for the pads thickness, or lack thereof.

If they are disc brakes, you have no capability to adjust them without removing the wheels, the calipers, and "shimming" the pads so they are thicker inside the caliper. If your pads are to thick, then you have the wrong pads, and if they are to thin to shim out, and safely stay inside the caliper, then yours pads are worn and needing replacement.