Is there a transmission plug in the transmission pan?

if you look under your car it will look like your engine oil pan, but usually on the opposite side. its usually on the drivers side of the car.

It is the reservoir at the bottom of the tranny, a flanged 'pan', usually attached to tranny with multiple small bolts around its perimeter.

trany pan is the oil reservoir for the trany. Also provides access to the filter, valve body & trany internal components

If it isn't on the pan, then there isn't one. You'll have to remove the entire assembly just to drain it. Replace the gasket if you do. If you're trying to drain it because you overfilled it, you can...

It is on the bottom of the pan.