Missing 1 Airpod
How to locate only 1 missing Airpod ?
Find My.. only locates the one airpod that I still have in the case
also unable to apply the disconnect L or R airpod for sending sounds.
You might not be able to use your iPhone to locate it if its not connected anymore.
You probably have to use your mark one eyeball.
This has more info, and information about how to order a replacement if you dont find it:
How to find your lost AirPods - Apple Support
Good luck!