Writing my own android app

Hello! I use the app ST BLE StartNet to control the STM32wb55 board's leds and even I could control others user's leds too. But I want to write my own android app to make a more advanced control of GPIOs. My question is how do I have to change the examples' codes so as to get data from my new app (for instance to control the blink speed of a set of led connected to GPIOs by buttons in my new app).

Thanks! I wait for you help