Thanks for bringing your question to Tundra Restaurant Supply Donna.
After speaking with the manufacturer, we think you're looking for the infinite control for this APW Wyott W-3V Countertop Food Warmer as opposed to a reostat. This unit does not come equipped with a reostat.
The part number for the replacement infinite switch for your unit is APW Wyott #55564. I've included this part below for your convenience.
Feel free to give a member of our team a call at 1-888-388-6372 if you'd like to talk specifics regarding your food warmer.