Now use the tweezers to slightly pry away the metal cover from the body. The cover is still attached by a solder tab to the board, so don't bend it too much. You only need to open it enough to remove the disc inside and to clean the inner contacts.

You may need to angle the device downward to let the metal disc inside drop towards the top of the button. Once it is in this position, you can use the tweezers to remove it.