Default Help with modifying an apk

So I have an apk that I would like to modify. It is seal communication to work with a piece of hardware. The controller it comes with uses the same protocol, what the controller does is stores 3 or 4 banks of presets the Android app only stores one bank. I would like to see if the functionality can be added I just don't know where or how to start.

Any suggestions appreciated

Oh I have tried to contact the developer of the app but have not heard back from them yet

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