The land transmission has two drain plugs, one under the transmission portion (hard to get at with transaxle in car), the other under the ring gear facing towards the engine. The fill plug for both the transmission and differential is even with, and in front of, the driveshaft opening on the flat side plate.
The water transmission drain plug is on the front of the water case just to the left of the fwd/rev selector hinge casting. The fill plug is a few inches above the drain plug.
Either fill through those fill plug openings or from the top vent caps until new transmission fluid flows from the fill plug openings.