I briefly had one once: IIRC, it was a pretty standard CdS meter (do you have the BM or TM - thread mount - version?).
Put battery in compartment, set ISO, move advance lever away from body to turn meter on (a la Nikon F2, FM...) and adjust your shutter & diaphragm until the meter pointer is centered.
Hello, I would like to share my experience with my "new " Icarex 35 CS camera. The meter prism is simple to operate. First yo need to install a fresh PX 625 battery, that is taking off the meter head from the camera body pressing the small buton on the left and sliding the head back, the battery door is of the swing type, battery has only one possible position, if is not installed properly the door can not be closed. Then attach the meter head to the camera sliding it foward until a "click" is heard. On the top there is a knob with film speed and shutter speed figures. Adjust film speed first pressing the center button and rotating the inner wheel until the desired number alligns with the arrows (ASA/DIN), then turn tne outer wheel until the desired shutter speed alligns with the front arrow. Then looking through the viewfinder while pressing the depth of field / meter activation button that is below the lens (on the left) turn the diaphragm ring on the lens until the needle on the top of the viewfinder in centered in the small circle. Presto ! that┤s it. Note: The big knob around the rewind lever/camera back open knob is only a reminder and has no effect on meter operation. Hope this helps.