I don't have the Master, but I do have the Super Technika V. Hope they are similar.
If you search the Linhof user manual, it will show you where to install the focusing cam. There you can find the focusing cam linkage to the the rangefinder. If you move the focusing cam linkage, the double image in the rangefinder should move. Then you are fine.
Regarding focusing cam: I bought two from eBay/KEH, none of them comes with the lens. The 135mm does not work with Symmar 135 convertible at all, while the 150mm works perfectly with my Xenar 150/4.5. Both lenses were Linhof select. I read there are compatibility between different Linhof models (and maybe between lenses as well).