They've buried it.
It's not hard.
First, make sure that your rangefinder is right. Fit all lenses you have at infinity and see if the rangefinder lines up to the same position, right or wrong (it should- this is your rough lens calibration)
No lens focuses past infinity that I've ever seen on this camera, in spite of what "Mamiya USA Tech Support says." If in doubt, use the 80mm for this.
Pop the little back cover next to the finder.
Turn the lens to infinity.
Look at a point (antenna work well!) nearly a km away.
Look in the back- the rased screw is the infinity adjustment. It's only a couple degrees to affect the rangefinder a surprisingly large amount. That's the screw you play with- the one farther in is the vertical adjustment, and here Mamiya warns that you shouldn't make an adjustment more than 1/4 of a turn- I concur, it's a sensitive one and if you have to adjust *at all* the use the smallest pressure you can.
Touch up the infinity adjustment, look through the viewfinder AFTER cycling the lens from close to infinity. Adjust.
The above cycle took me 15 minutes to get my rangefinder *exactly* co-incident at 1km when I was last in Lisbon. The rangefinder was far better adjusted than when I thought it was "right" before hand- contrast improved- making me suspect that the rangefinder was slightly off in the vertical.
Keep the screwdriver in the bottom of the bag, tucked so that it can't scratch.
It's an absolutely wonderful camera, fun, light, and the pictures are probably the best ever produced by any camera- the lenses are probably the best... &c.
Have fun!