iPhone 6 plus and BlueAnt Z9i pairing

Howdy sok lee,

Linked below you'll find an article that details how to go about pairing your headset with your iPhone 6.

Set up and use third-party Bluetooth accessories
https://support.apple.com/en-us/HT204091

Should you be unable to pair your headset, the next article linked details a number of troubleshooting steps that can help get your iPhone and headset to play nicely together.

Get help connecting a Bluetooth accessory with your iPhone, iPad, or iPod touch
https://support.apple.com/en-us/HT201205

Sincerely