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 AdjusterSteering Switch Inspection
Without Bluetooth System
WARNING:
Handling the air bag module improperly can accidentally deploy the air bag
module, which may seriously injure you. Read the air bag system service warnings
and cautions before handling the air bag module..
1. Disconnect the negative battery cabl ...
Brake Fluid Pressure Sensor Inspection
1. Switch the ignition to off.
2. Install the SSTs to the master cylinder (secondary side) as shown in
the figure.
NOTE:
When installing the SST (49 D043 0A0) to the master cylinder, use
a commercially available flare nut wrench (flare nut across flat 12 mm {0.47
in}).
...
Door Lock Switch Inspection
1. Disconnect the negative battery cable..
2. Remove the inner garnish..
3. Remove the front door trim..
4. Remove the front inner handle..
5. Inspect for continuity between the door lock switch terminals using an ohmmeter.
If not as indicated in the table, replace the door lock ...