I have an 88 Dakota, and I just recently had to do the same thing.
Remove the far drivers side bottom dash panel and up under there is a small non-descript box it's like 1inch thick by 3inches tall I believe its got a blue cover on it,when you see it youll know it. there is a small hole right on the front, in that hole is a button that resets your Maint.Req light. I had to use the insides of an ink pen to get it the hole is pretty small. Just press and hold for like 3-5 seconds. hope that helps
well I found the blue box. It is to the left of the steering wheel and is light blue. Has a square opening on one side of it and on the top has the small hole . That hole is where i used a cotter pin to push the button down . I think I had to have the ignition on engine not running for it to take. But it is out for now.