How to get new coverage

If you have a valid AppleCare+ plan you purchased on your iPhone, it can, in some locations, be renewed on a month to month basis, IF you renew it within 30 days (not one day more) after the plan expired.

See this for help if you qualify --> Extend your AppleCare+ coverage - Apple Support

If you didn't purchase an AppleCare+ plan or it expired more than 30 days ago, there is no option to get new coverage from Apple.

If you are included in the countries that offer an extended plan it should come up in general>about after your apple care + has expired, as an option to purchase the extended apple care + on the iPhone. I will anyway suggest you to give a call to the Apple support, before the expiring date to confirm when you can purchase it exactly.