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 AdjusterNon Return Valve Inspection [Mzr 2.0, Mzr 2.5]
WARNING:
Fuel is very flammable liquid. If fuel spills or leaks from the pressurized
fuel system, it will cause serious injury or death and facility breakage. Fuel
can also irritate skin and eyes. To prevent this, always complete the “Fuel
Line Safety Procedure”, while referring to ...
Electrical System
Electrical Parts
Battery cable
Before disconnecting connectors or removing electrical parts, disconnect
the negative battery cable.
Wiring Harness
To remove the wiring harness from the clip in the engine room, pry up the
hook of the clip using a flathead screwdriver. ...
Camshaft Position (CMP) Sensor Removal/Installation [Mzr 2.0, Mzr 2.5]
CAUTION:
When replacing the CMP sensor, make sure there is no foreign material on
it such as metal shavings. If it is installed with foreign material, the sensor
output signal will malfunction resulting from fluctuation in magnetic flux and
cause a deterioration in engine control.
...