Hey there MartinnCs,
Thanks for reaching out to the Apple Support Communities. To get started, per the 'Related Article' that was shared on this thread, the best option would be to reach out to Apple Support directly for help with updating the purchase date of your AirPods.
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:
- Your AppleCare agreement number
- The device serial number
- Your sales receipt
You can use the 'contact Apple Support by phone' link above to call the best number for your region, or reach out to Apple directly at this link here: Get Support - Apple
We hope that's able to help.
Have a great day!