These locks are intended to help prevent children from accidentally opening the rear doors. Use them on both rear doors whenever a child rides in the rear seat of the vehicle.
If you slide the child safety lock to the lock position before closing that door, the door cannot be opened from the inside. The door can only be opened by pulling the outside handle.

Locking, Unlocking with Door- Lock Knob
Trunk LidMazda 6 Owners Manual: Rear center seat belt removal/installation
Caution
The ELR has a spring that will unwind if the retractor's cover is
removed. The spring cannot be rewound by hand. If this occurs, the ELR will
not work properly. Therefore, do not disassemble the retractor.
4SD
1. Fold the rear seat back.
2. Remove the rear package trim.
3. Re ...
Mazda 6 Owners Manual: Selector lever disassembly/assembly
1. Disassemble in the order shown in the figure.
2. Assemble in the reverse order of disassembly.
Connector Disassembly Note
1. Insert a thin piece of metal from the terminal side of the connector, and
press down the terminal locking tab.
2. Pull the terminal out of the connector. ...