L1 Mix App
Place your finger in the middle and then drag your finger up and down over the control (like you would if it was a slider). That works well and it is easy and intuitive.
Tap in the middle to toggle through Volume, Treble, Bass, Reverb - OR Tap on the words Volume, Treble, Bass, Reverb Don't try to rotate or drag around the control. That's not how most virtual digital controls work.