You also need to remove the lens of the rangefinder window. Unscrew the chrome bezel, and the the actual lens can be accessed and carefully pried out. This is the part that you turn to correctly set the vertical register of the RF moving image. Note carefully its position before removing it. It will be necessary to readjust it (by rotating it) when putting everything back together, and if you put it back 180 degrees wrong you will find that it messes up the HORIZONTAL position. With this removed, you now need to unscrew the ring into which it fits. I use a flat piece of steel filed to fit the grooves in this part without touching and screatching the camera top. When reassembling the camera, adjust the vertical RF position first and then the horizontal (which is behind the large screw on the front). The moon is the very best target to set the RF at infinity.
It's a lot easier than it sounds!
Cheers,
Dez