Long-press the control dial for two seconds to enter Bass mode. You’ll hear a tone and the LED light will stay lit while you’re in Bass mode.
Turn the dial clockwise or counterclockwise to adjust the bass. After you’ve fine-tuned the bass, long-press the dial to exit — you will hear the “exit Bass” tone.
NOTE: The dial will automatically return back to the system volume mode after 15 seconds without adjusting.