I cant update purchase date

Click on this link to read how to update your proof of purchase --> Update your proof of purchase - Apple Support

To update your information contact Apple Support by phone. Tell the advisor that you need help with your Apple Limited Warranty or AppleCare plan expiration date.

Here’s what you need when you call:

- The device serial number

- Your sales receipt

- Your AppleCare agreement number

Note that if you bought them from a third party reseller who is not an official Apple retailer, the warranty started on the date the reseller bought them from Apple, not when you bought them from the reseller (unless the reseller offers their own warranty).