The RB lenses have an auto manual selection knob on each lens that allows you to release the shutter at the same time you press the release button on the bottom right. However, if you switch that knob to manual and screw in a cable release into the knob, when you press the button on the bottom right, only the mirror goes up. Then, you have to press the cable release cable button to release the shutter on the lens. You wait a second or two so the mirror shake is gone before you release the shutter.
There is a dial cable release from Mamiya for this purpose. But you can do it fairly simply with a ordinary single cable release as i described.