How to find my AirPod
my AirPod missing from the case
If you are lucky, the missing pod might appear in the find My app on your iPhone or iPad, and it might have enough battery for the app to guide you close then play a sound to help you find it. Otherwise you have to search where you think the missing AirPod might have been lost, working the old fashioned way with your eyes.
if you fail to find the missing device it is possible to purchase a single item as replacement. AirPods Repair & Service - Apple Support