The metal cover is found by Aline Cedrac in Alone in the Dark: The New Nightmare.
The New NightmareEdit
The metal cover is inside the tomb of Jeremy Morton, in the crypt of the Morton family. An inscription on the coffin suggest its use: 'Only a symbol of light will open the tomb.' In fact, by combining the metal cover to the torch, you will get a smaller but much more precise beam of light, with which activate a reflective crystals mechanism that open the tomb of Richard Morton.