Connect your Android device to your PC via USB and use it as a USB MIDI controller.
Can be used as a substitute when there is no physical controller.
The MIDI setting of the software on the PC side is required.

You can use another application (MIDI Controller Config) to change the MIDI signal.
https://play.google.com/store/apps/details?id=com.sovemidicontroller.midi.config

It's easy, but I've described how to use it in my blog.
https://iimhmt.blogspot.com/2020/04/midi-controller_28.html