How do I extend my AppleCare for iPhone 11?

See if this helps: Extend your AppleCare+ coverage - Apple Support

Hi PleasehelpmeAppleCare,

After getting the iphone you have a limited time till you can get applecare, once this has collapse you can not get apple care for your iphone anymore, this also goes for once you have had your 2 years of apple care you can not get a new apple care to take it on for anther 2 years.