I want purchase right side airpod how I can it

If it's still under warranty (or you have AppleCare), you can possibly get it replaced at no charge. If it's out of warranty or you just want to buy a replacement, then go to Apple Support: https://support.apple.com/airpods/repair/service

I don't believe you can just buy a single AirPod without using Apple Support.

https://support.apple.com/airpods/repair/service

just I want buy right side AirPod