You can make the special tool by yourself, if you are well with your fingers and handy work.
There are some photos floating the net of a topless M, showing the mechanism and the special tool for a better understanding, what to do, and when better decide, to let a pro do the job.
I adjusted the vertical alignment on my M8.2 with a properly made tool, as it has been off by a mile, when I bought it new. It is perfect now.
Basically, you can do the special tool with a jewelers screwdriver, a diamond file, some fine sandpaper and if needed some electrical tape.
You have to file one corner out of the screw driver blade (in a very special measurement, that fits your camera), de burr any sharp edges with the sandpaper and use the electrical tape, to prevent your camera from unprofessional track marks, doing the operation (that's why Leica wants to prevent from unauthorized fiddling and rightly so, as many people think, a butter knife will do ;-) ).
You fit the special tool/ special screw driver with the tip into a fitting in the set mechanism and move a fork shaped metal sheet up or down by turning the special tool around the tip, engaging the "fork" with the out of center cam.
Good luck and leave your fingers out of there, if you are not sure!