You won't. Just desolder each pin, and then carefully remove it.
Well, you could try. Go to the positive and negative terminals and bridge them with a resistor. It will sap the charge, but it isn't high voltage (3 to 5 vdc) so it isn't a problem to desolder and remove.
So I cleaned the board as instructed, let it dry, reassembled, and powered up. Game will now not start a game, I cannot get into test mode, and digital display now looks like this. I guess I'll be starting a repair thread.