Be sure to clean up any residual solder or flux, if used, and clean the area with a Q-tip and rubbing alcohol or PCB cleaner to clean up the mess.

You will notice that the PCB itself looks kind of nasty. When I did this repair I cleaned the entire system inside and out. No matter how much I rubbed a Q-tip with PCB cleaner on it those white looking scuff marks still wouldn't come off. Don't be surprised if this happens to you. Better yet, don't waste your time :)

Once the mess, if present, is cleaned you can insert your replacement 8mmx8mm switch and solder the pins to the underside of the main PCB.

Once the soldering is complete then so is this repair. Simply reassemble your device and hit your power button and it should power up as if there was never a problem. If you can't keep the original consoles alive at least continue the great memories of your favorite 8-bit games. Happy Retro Gaming!