Controll screen by python

Hello my friends. I'm developing an app to control a system based in raspberry pi4. My system has many procceses and i want to show a diferent screen in the app for each proccess, but they don't depend of a time lapse (because each takes a random time depending of the process). is there a way to send and order from my python code to the apk that orders when the screen should change?, please let me know if you know how.
P.D. by this time i only know how to send a request from app to python to activate my system, but no the opposite thing.