Use keypad on Chatter 2

[tomhanax]

I have several Chatter 2.0 (from Circuitmess) and they are nice devices. However, to be more practical than toys, they could be flashed with meshtastic. And it works great. BUT.. I miss the ability to use keypad. The whole point of this device is ability to compose messages without additional device.

So the question: what is the best course of action to add the ability to compose messages (like T-Deck)? I am pretty new in this "Arduino C++ world". Can somebody please give some pointers, where to start looking? I found some traces in kbMatrixBase.cpp and kbI2cBase.cpp, but I really do not know how to start.