Save your AirPods’ serial number to replace lost parts
“Take a screenshot or picture of your AirPods serial number. You can’t replace any parts without it.
Do this when you first get them!!
You can take a picture of the box or a screenshot from Settings > General > About > AirPods so that Apple can pull up the serial number.
If you lose the case and don’t have the serial number anywhere, you can’t even replace the case without it.” The Full Story