Some models of Ford transmissions have a torque converter drain plug that is accessible when the pan is off.
The usual way to flush is through the cooler hoses. A machine with a dual-chamber vessel is connected to the hoses, one chamber is filled with new ATF, and the engine is run. The pressure of the ATF being pumped from the transmission fills the empty chamber and forces the new ATF from the other chamber into the return hose and into the transmission. Cheapo shops just clamp the hose with vise-grips while they add new ATF down the filler tube.
I prefer to drain the pan and refill before the flush. Best, of course, is to remove the pan, clean it, and renew the filter, if fitted.
Shade tree mechanics can do the same job by connecting a short hose to the cooler hose from the transmission. After draining and refilling the pan (if feasible), idle the engine, pump two quarts of old ATF into a jug, stop the engine, add two quarts of new ATF down the filler tube, pump out two more quarts, etc., etc., until a full exchange is complete, 14 or 15 quarts on most transmissions.
I'd like to use 6 oz. of Auto-Rx in the transmission for 500 miles before the flush. If the transmission sump doesn't have a filter I'd add a filter in the cooler line.
Ken