If you hear a rubbing noise from the front wheel, the brake line may be too tight. 

The Kqi2 kick scooter uses a drum brake and only has a mechanical brake in the front. Adjusting the brake is easy by following the steps below:

1. Loosen the screws fixing the front brake cable.
2. Adjust the rocker arm position. The more upward the rocker arm, the tighter the brake and vice-versa. The lower the rocker arm, the looser the brake.
3. Tighten the screws for fixing the front brake line.
   
   

In addition, the electronic brake can be adjusted by adjusting the regenerative braking sensitivity through the NUI App. You may choose between three levels: strong, medium, and weak.

More detailed instructions can be found here.