(my big big thanks again Andreas)
i tried to do the job the simple way...
i located the "small hole behind the back door just under the moving prism"
--the small hole is covered by a screw cap, have to unscrewed to reveal the hole. however it really is tricky to turn the screw
so i took the further step: take off the whole rangefinder module.
i noticed that the screw for adjusting the horizontal alignment is damaged (by me may be?),
i have to use pliers to turn it.
after playing it for a while i (kind of) figured out the mechanic of the RF and i finally adjusted the alignment.
i put the top back only to find the meter stop working
the needle on the top plate stop moving (stayed on the top position)
and the indicator in the viewfinder is totally out of sight
it scared the xhit out of me...
i have enough experiences on screwing up cameras, i know i have to stop for a moment and go out for a walk (so that i can do no more wrong, and to breathe, stay cool and THINK!)
i went back 2 hours later, i keep calm and study the whole RF module again.
i discovered there is a "catch" under the meter to control the aperture and the meter needle.
so with great care i attached the catch back --it's very tricky because you have to do it at the same time when you put the module back (and
you also have to put the RF mech in position with one single action)
i tried many times in cold sweat before i finally put the module back successfully,
now i am a happier person. the next step is to shot a first roll.