Now, we just need to install the Circuit Playground Express & Electret Microphone board in the Piano Toy-Con.
Push back the large cardboard plate that supports the Switch until the interlocking front lip pops up.
Once the wires are routed, push the front lip back in place with its tab locked into the backing plate.
Use a small piece of double-sided tape to stick the the LiPo battery to the back of the Circuit Playground Express.
Use another piece of tape to secure the LiPo battery and Circuit Playground Express to the top of the piano.
Install the right Joy-Con in the holder at the back of the piano and place the Switch console in its spot at the center. Set the Switch's volume all the way up and start up the Piano Play mode in the Labo Variety pack cartridge. Now - you're good to go!
Now, when you play the piano - you'll have a light show with every performance :)