The traditional way to make a small adjustment is to carefully bend the small metal tab where the struts meet the sliding portion of the rangefinder. With no film in the camera and a small piece of ground glass taped into an old film holder, mount the camera on a tripod, and move be bellows to the infinity setting. The object should be in sharp focus when checked with a magnifier. Now check the rangefinder. That should agree. If not, carefully, bend the small tab left or right so that it does agree.
You can then repeat the same experiment at a close distance, perhaps 10 feet. Carefully check the ground glass. Then the rangefinder. Perfection is impossible, as the rangefinder does not perfectly track focus, but it is very close and certainly good enough.
If you don't have a ground glass, use frosted tape on a small glass slide or other flat piece of glass taped into the film holder at the exact place where the film would be. You won't get the entire view, but enough to perform the adjustment. Place the tape on the lens side of the glass. An image will form on it.
Are you sure it is out of focus? Try a tripod and a subject at infinity and if the error is small you might live with it or gently tweak the tab. Notice that you can slide the rangefinder arm all the way to the left (looking at the camera from the front) and that is closest focus. It should spring back without sticking. Try doing that while looking through it and you will see which way to go. It should not be far off, and if it is, look for some other damage, distortion etc to the camera struts.
Get some Fuji FP100B for it and try that before it is all gone!