If its cowansim it’s usually in the manual in the first few pages.
If it’s flyinside 206 its also in the manual but down a bit. They say:
You’ll need to click on the Idle Release button to then fully close the throttle and shut down the engine. You may also bind “DECREASE COWL FLAP 3” in MSFS to trigger the Idle Release button.
So you’d need to be more specific about which heli.