I own three of these, one of which is in fine working order.
Have you been successful in guessing your way through? If not, I have a handbook, but unless it requires some unusual adjustment, you have only a few simple things to do.
Working from memory...
First off... are the optics clear, and does working the halving adjustment worm cause the images to slide against each other smoothly? If not, you have some refurbishment/cleaning/repair to undertake and I can't help you. BEWARE THAT SOME OF THESE ARE CLAD IN ASBESTOS.
Now you need to adjust the halving alignment so that the two views precisely split the image space so that no part of the view is lost and (conversely) no part of the view appears in both halves of the image. You only need to do this if, when looking through the device you sense that one or the other of these maladjustments is in force. If you see a smooth transition between halves when
This is perhaps best done with the device on a stand, and it can be frustrating. The mechanism for performing this adjustment is likely under a flip-up or rotate-to-open little cover to ward off inadvertent changes in setting. Details vary by the RF.
Once the halving is good, all you need to do is obtain a single range on an object of known distance and adjust the convergence so that the known range is indicated when a "cut" is perfectly set on the RF. The RN suggested using the edge of the moon for this (setting the RF to "infinity"), but I find it more appealing to use something at about 500 yards range.
Once this is done, you are good to go. Ranges obtained will be exceedingly accurate out to 400 yards (say 1% error), pretty darn good to 800 (2% or so), and then fall off rapidly. Over 5,000 yards you can expect 20% errors or so.