That depends on your Midi setup on the host computer, try running MidiKeys on the computer first and get it up and running with that: https://flit.github.io/projects/midikeys/ (or similar if you’re not on MacOS).
If still no luck move the conversation to an issue on the repo: https://github.com/orllewin/playdate_midi_bus - it’s a bit out of scope for this forum.