On the 7AT there are two plugs. One is the main drain plug, and there is another small allen hex drain plug that is the set plug for fluid level. There's an adapter you can get to connect to the main drain plug, and pump in half a qt of fluid into the trans. Get the fluid temp within spec, and pull the level plug, until it comes to a slow drip. That's how you check and set fluid level.
To exchange the trans fluid first get vehicle to temp, drain fluid from main plug, measure what you take out, pump back in the same amount taken out with clean fresh matic S fluid, run vehicle to temp, going through all the gears a few times, then repeat this same process 2 - 3 times. On the final fill up put in a half qt more than what was taken out to set to the correct level using the previously mentioned fluid level check.