You can buy the crows foot wrench that size - advance auto also sell it, you can also use a toilet wrench if you wish, the nut is there to "somewhat" provide a small friction so that the shaft does not quickly slide on the splines. It should slide but with some effort - thats the idea.

You can also use a chain wrench or even a rubber band oil filter tool on it.

You can move the manual valve all day long with your hands and nothing will happen - however you only need tomove it one detent to get in reverse.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)