You should see a hole to the left of the temperature control knob with a plastic plug covering that hole. Remove the plastic plug. Look through the hole and you'll see the manual advance dial for the defrost timer. Use a slot screwdriver to advance that dial until the compressor shuts off (if the compressor isn't running, wait for a few minutes with the refrigerator door open until the compressor starts). Once the compressor shuts off, the defrost timer should be in the defrost mode. If the timer doesn't advance out of the defrost mode, replace the defrost timer: searspartsdirect.com/part-number/WR9X520/0046/363.html
Unplug the refrigerator before replacing parts.