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: Inside Trunk Release Lever (Some models)
Your vehicle is equipped with an inside trunk release lever that provides a means
of escape for children and adults in the event they become locked inside the trunk.
No matter how careful adults might be with keys and locking their cars, parents
should be aware that children may be tempted to p ...
Mazda 6 Owners Manual: Rear seat disassembly/assembly
4SD
1. Disassemble in the order indicated in the table.
2. Assemble in the reverse order of disassembly.
5HB
1. Disassemble in the order indicated in the table.
2. Assemble in the reverse order of disassembly.
...