Depress the button on the seat belt buckle. If the belt does not fully retract, pull it out and check for kinks or twists. Then make sure it remains untwisted as it retracts.

NOTE
If a belt does not fully retract, inspect it for kinks and twists. If it is still not retracting properly, have it inspected at an Authorized Mazda Dealer.
Fastening the Seat Belt
Front Shoulder Belt AdjusterMazda 6 Owners Manual: Rear Cross Traffic Alert (RCTA) (Some models)
The Rear Cross Traffic Alert (RCTA) system is designed to assist the driver in
checking the area to the rear of the vehicle on both sides while the vehicle is
reversing by alerting the driver to the presence of vehicles approaching the rear
of the vehicle.
The Rear Cross Traffic Alert (RCTA) ...
Mazda 6 Owners Manual: Mazda Radar Cruise Control (MRCC) (Some models)
The Mazda Radar Cruise Control (MRCC) system is designed to maintain headway
control*1 according to the vehicle speed using a radar sensor (front) to detect
the distance to a vehicle ahead, and by presetting the vehicle speed between 30
km/h (19 mph) and 145 km/h (90 mph), the driver is freed ...