Banglerun with a custom mobile app

Ok i think i found a way to modify the app, it is a little bit twisted but it should work. I'm going to explain how for future people that will might have the same problem.
After installing all the package nedded (see preavious posts to understand), you can modify the code inside \src folder. After that, running the rollup.config.js file in that way:

rollup --config  rollup.config.js

it will be created a new file app.js with your modifications. After that, the file app.js can be copied and pasted in Espruino IDE and finally runned in bangle.js.

I don't know id it is the best way to do that but it works.