If you want to provide your own audio file for this music box you can easily swap a new one in place of the one provided here.
Audio files can be gathered by any means you like, but they will all need to be formatted as mono 16-bit PCM WAV at 22,050 Hz to be recognized by CRICKIT.
Depending on your location, you may need to adjust your music box's responsiveness to light. This can be done in Mu, by increasing or decreasing the default value of
3000 (responds to bright light) or down to
1000 (more responsive to dim light).
If you enjoy CircuitPython and want to continue learning you can find lots more CircuitPython projects on the Adafruit Learn System.