How to communicate android app(from Unity) to arduino.

Hi, I have built an app which communicates to arduino via serial. I exported this app to android. Now how can I communicate this app with arduino.
The COM ports are already decided on the Unity app. How can I go further.

I think you change the port setting on the Arduino side.

Have you solved this problem yet? If yes please let me know how did you do it… Thank you.