I don't have a tranny fluid reservoir on my car, I wish I did. There are two plugs in the drivers side of the tranny casing, drain and fill.
Drain the the fluid out via the drain plug, put it back in, take out the fill plug and pour ATF through the shifter hole until fluid comes out of the fill plug hole, replace the plug and your good to go.
I think it did take about 5 quarts plus a shot of friction modifier.