this is going to be a problem. I have found only one link to a manual, a copy from Switzerland, which is in German language, of course:
But as far as my experience goes, just buy a cheap roll of film and start experimenting. Usually these ZI cameras are sturdy. I have so far used an ICA plate folder, a Nettar folder, a Taxona, a Contessa LKE, an Ikoflex I and very lately a Contax II without coming across any manual. Then I got one for the Taxona at least, at a camera flea market.
Before you buy, be sure that the rangefinder itself is in good alignment.