Horn LO

Disconnect the negative battery terminal. (Refer to NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
Remove the front bumper. (Refer to FRONT BUMPER REMOVAL .) (Refer to FRONT BUMPER INSTALLATION .)
Disconnect the connector.

Fig 1: Identifying Low Horn, Connector And Bolt With Torque Specification
Courtesy of MAZDA MOTORS CORP.
Remove the bolt.
Remove the horn LO.
Install in the reverse order of removal.