Something like this would be the steps, I list the steps to follow:
1) Drain the carter oil, move the lever in all its positions to get the possible oil trapped in the labyrinths of the transmission, do not boat the oil, examine it that there is so much water.
2) You change the filter.
3) Proceed to fill with new oil, pass the key without turning on the engine and move the lever so that the new oil penetrates the labyrinths.
4) Disconnect one of the radiator hoses and prepare the recipient of collection.
5) Turn on the engine and observe the oil that comes out through the hose, when you see that the coloration to bright red is the new oil that comes out, turn off the engine, in this step it is good to have another person to help you.
6) Reconnects the hose to the radiator, turn on the engine again and wait as 5min, move the lever in all its positions and proceed to measure the oil level, it must be in the low marks of COLD, if it is missing completely, leave for 10min more and then measure again at the level.
So far the steps of an oil change for the transmission, now the inspection part comes, check whether in the last measure of oil there are bubbles, water droplets or other abnormality, now with the oil that is taken out through a strainer to see if there are no particles of metals or others, the important thing apart from removing the water from the system, is that there are no damage due to the effect of the water, if there are no solid waste. softness like turning the apple. Any anomaly turns off the engine. If everything goes well I would do another oil change only a week, to eliminate any vestige of moisture. Excuse me the extended response, tell us how it went. Luck.