This step is only necessary if the rangefinder is significantly off horizontally.

Remove the RF assembly following the Leningrad disassembly guide.

Screw the eyepiece (blue box) back into the RF assembly for viewing during the adjustment.

Loosen the screw circled in green. Carefully shift the arm secured by the screw to adjust the mirror position. Caution: the adjustment is very sensitive.

Tighten the screw, temporarily put back the rangefinder assembly into the body. Confirm the rangefinder patch is in the correct ballpark with a lens.