Remove the two screws from the locations circled in red. This will allow you to remove the power switch board.

Be careful not to pull hard on the board once it is removed from its holder as the ribbon cable connecting this board to the main board is soldered and does not have a removable connector.

Once the power switch circuit board is unscrewed, a small plastic piece can then fall out of the casing. This piece serves to press down on the power switch when the lens cover of the mouse is closed.