As stated before here, its a sealed system.However, if you are going to check the fluid level, look at the right side back end of the transmission and theres a hex plug. You can remove it and if fluid flows out its full.
Most of these modern BMWs are "sealed for life". I believe they started doing this before 2000.
They argue that you do not need to replace or replenish your trans fluid. Most techs recommend to replace at 60K or so, to be conservative. You'll probably want professional help for a full fluid change.
Do not remove the plug with the engine not running. You must have the car level, running, between 30 and 50 degrees celcius ( basically cold start with a load on i.e high beams radio and a/c full blast),and the engine in neutral after cycling through all gears(with e-brake set). Once you have all those requirements met you remove the plug. proper fill level should have fluid barely running out of the hole(not the hole in the pan but in the side of the back just above the pan). Fluid for these models is very expensive so price check before draining for an unnecessary service.Also you must have a pump to pump fluid into transmission before it gets over 50 degrees celcius. maybe leave this to the shop or just leave it alone like the label says.