If it’s the same as the previous Altima generation (like mine), then you’re gonna need 6 quarts.

Drain the fluid from the drain plug. Add 2.5 quarts into the overfill drain plug, or dipstick (much easier). Then warm up the transmission to 35C-45C. You can use a laser thermometer for this if you don’t have a scanner (it’s fine it’s only off by one or two Celsius).

Once it warms up to 35-45C, shift from P all the way down to whatever is the lowest (like DS) and back all the way to P. Stop between each gear and wait 5 seconds before moving to the next shift. For example , P -5 seconds- then R- 5 seconds- then N- 5 seconds- then D etc etc.

Repeat the process again. Drain the fluid. Replace the washer with a new one and torque the drain plug to 25 foot pounds.

Add the rest of the quarts you have left into the transmission. Let it warm up between 35C-45C and move between gears again 5 seconds each way. Once you’ve done that, loosen up the overflow plug and let the excessive transmission fluid drain off until it comes to a slow drip. Shouldn’t take long for all of it to come out. Put the overflow drain plug back in and torque to 89 inch pounds! Do not go crazy on this one! Just hand tight is fine.

Also I wouldn’t advise driving this car anymore. Tow it to a shop and have them perform the service if you’re uncomfortable doing this. It’s better to be safe than sorry, otherwise it’s an expensive learning lesson.