how can I claim my lost item with apple care?

Which Apple care do you have?

AppleCare+ does not cover You for loss or theft of Your device, or for failure due to defects in Your device, although such failures will be covered separately either by Your rights under consumer law or the Apple Limited Warranty, or by Apple itself during the same period as the AppleCare+ Coverage Period even if You did not purchase or lease Your Apple product from Apple (as set out in clause 5.1.9).

https://www.apple.com/legal/sales-support/applecare/applecareplus/041520_applecareplus_uk_tc.pdf

If you had theft and lost coverage, see the link below.

File an iPhone Theft and Loss Claim - Official Apple Support