To be precise: Look for a small, usually rectangular, valve near the back of the intake manifold. It will likely have a vacuum line connected to it and possibly a wire for a solenoid. It's often somewhat difficult to see, tucked away amongst the hoses and other parts. You may need a flashlight and possibly some maneuvering to get a good look.
To help you find it:
* Consult a repair manual: A Haynes or Chilton manual specific to your 1992 Plymouth Voyager with the correct engine size will have diagrams showing the exact location. This is the best way to ensure you find the correct part.
* Use online resources: Search for "1992 Plymouth Voyager [3.0L or 3.3L engine] EGR valve location" along with images. You might find photos or videos showing its position.
Remember to be cautious when working near the engine as it can be hot.