Constant speed propellers are controlled using the propeller lever and the throttle lever. Typically the prop sets the RPM of the propeller and the throttle sets the engine manifold pressure. The propeller then automatically adjusts itself to maintain a constant RPM. For one of the (real) aircraft we had a typical setting was 2500 RPM and 25" of manifold pressure as an example, you'd adjust the two controls to maintain that.
Thanks for the clarification. What do you mean by one of the aircraft you had?