To be certain:
1. Consult your owner's manual: This is the most reliable source. The manual will have a diagram showing the location of the dipstick and may even have instructions for checking and changing the fluid.
2. Look around the transmission: The transmission is a large, usually rectangular component in the engine bay, towards the rear of the engine. The dipstick is generally near the top or side of the transmission. It might be color-coded (often red or yellow) or have a noticeable handle.
3. Check online resources: Websites like Chilton or Haynes offer repair manuals for specific vehicles. Searching for "1991 Chrysler Plymouth Voyager transmission fluid dipstick location" may yield images or instructions.
Important Note: If you can't locate the dipstick, do not attempt to add transmission fluid without knowing precisely where the fill location is. Adding fluid to the wrong place can cause serious damage. It is best to consult a mechanic if you are unsure.