Ok I find the user guide:
2. How to work with motor hall-sensor malfunctions:
The controller will detect motor hall-sensor failure and make 2 beeps of sound, and then it automatically
enters into sensorless control mode. Turn the throttle to run the motor. You may need to push/pedal the
ebike or vehicle a bit in case the motor does not move from stall (This is sensorless control limitation, but
happens seldom).