Here are the specific instructions from the Beretta web site: (copied from Shotgunworld
This switch is only found on the current 471 Silver Hawk side-by-side shotgun. This manual covers both over-under and side-by-side shotguns. Instructions to operate this selector switch are shown in the manual:
Caution: Make sure the firearm chambers are empty and the firearm is unloaded first.
1 - Remove the fore-end by depressing the button at the front and pulling the fore-end down and away from the receiver .
2 - Locate the selector switch inside the fore-end on the left - rear end of the fore-end iron, it is marked E and M.
3 - Locate the small round hole drilled into the selector switch and install a punch, small screw driver or similar tool into this hole - move the switch forward to E for automatic ejection of the shells or towards the M for mechanical extraction of the shells.
4 - Reinstall the fore-end on the shotgun.
Not sure if you knew this or not.
Might be the selector needs some tlc ?
Rob