how to extend my warranty

AppleCare+ adds one additional year to your warranty, for a total of 2 years coverage. But AppleCare+ for any Apple product must be purchased and registered within 60 days of purchasing the device you want to cover.

You must have brought Apple care ? Have you when brought the iPhone?

No Apple warranty or agreement can be extended.

If you are within 60 days of purchase, you can buy an AppleCare+ or Apple Protection Plan agreement.