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 AdjusterSeat Weight Sensor Inspection [Two Step Deployment Control System]
CAUTION:
If any of the following work is performed, perform the seat weight sensor
inspection using the M-MDS.
Removal of the passenger-side seat
Loosening and retightening of passenger’s seat fixing bolts
Or, the vehicle is involved in a collision
...
Quarter Window Glass Installation
WARNING:
Using a razor with bare hands can cause injury. Always wear gloves when using
a razor.
CAUTION:
If a door is opened or closed when all the window glass is closed, the resulting
change in air pressure could cause the sealant to crack preventing the proper
insta ...
Front Drain Hose Installation
CAUTION:
If the front drain hose is pinched or bent anywhere, the water in the hose
may not discharge and enter the inside of the vehicle. During and after installation
of the trims and the headliner, always make sure there is no interference with
the front drain hose. Fix any probl ...