I've done this with a Fuji 6x7 rangefinder, and all I can remember is that it was not at all difficult. I don't have the camera any longer, so I can't check.

Make sure there isn't some way to make the adjustment without taking off the housing. (e.g. removing a screw could open a little hole in which to insert a screw driver).

Is there some kind of covering over the center of the cocking lever? If so, removing it might reveal the screws or whatever that hold down the lever. My experience has been that left-handed threads are used on any central screw that holds on a winding knob or lever. [... discovered by twisting off the first one I tried to undo...]

My recollection is that the Fuji rangefinder had a vertical adjustment (to get the images to align in the vertical plane when the horizontals came together) which was on top of the rangefinder "guts" over on the right, and a horizontal adjustment to set for "infinity". I don't think there was any linearity or second-distance-focus adjustment. I think the horizontal/distance adjustment screw is adjusted from the front of the camera. It's been a long time. But it's obvious once you see what's inside.