Press the red button on the seatbelt buckle and then let the belt retract. If the seatbelt does not retract fully, feed it in by hand so that it does not hang loose.
Seatbelt - loosening
Heavy braking can have serious consequences if the seatbelts are not used. Ensure that all passengers are using their seatbelts during the journey.
Loosen the seatbelt when the car is stationary.