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 AdjusterFuel Pump Unit Disassembly/Assembly [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 ...
Seat 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
...
Cargo Compartment Light Removal/Installation
1. Disconnect the negative battery cable..
2. Insert a tape-wrapped fastener remover into the service hole and pry with
the screwdriver in the direction shown by the arrow to remove the cargo compartment
light.
3. Disconnect the connector.
4. Remove the cargo compartment light.
5 ...