Update Arduino variable from MIT App input?

Noob here. I have a single potentiometer hooked up to an Arduino and have it displaying to serial, therefore displaying the value on a very simple MIT app. I need help knowing if it’s possible to use the app to return values to the Arduino, updating the variables in the Arduino sketch.

I have variables set up in my sketch and display numbers 0 to 10 based on the rotation of the potentiometer instead of 0 to 1023. This is all good so far, but I want to be able to calibrate where my 0 to 10 numbers are, as they aren’t all linear and may need to change based on the usage of my device. I roughed this out with buttons on a breadboard and my code is successful for that, but I want to keep the device small so am looking for an app interface.

I’m using an HC-05 and have successfully linked to my app to display the values on the app, so I know the bluetooth connection works and my project is successful with the exception of being able to calibrate the device through the app as opposed to analog buttons.

Any help on what I may be missing regarding updating the variables through bluetooth so I can calibrate this thing would be helpful. I’ve tried looking through tutorials, other posts, searching in the forum, etc. but maybe I’m using the wrong terminology. Thanks in advance!