Keep the left airpod in the case and case is closed. On FindMy, press your AirPods. Press ‘directions’ to get you as on top of the location of that right AirPod as possible. go back one screen, and you will see “Play Sound”. When you hit play sound it gives you three buttons: Left - Stop - Right. Press Right (obviously

). A sound will play from the right AirPods Pro, AirPods 3 and I believe ? AirPods 2 (I think ??? you’re SOL if they are OG AirPods). Don’t play the sound until you’re relatively certain you’re very nearby it. Save the juice in the battery. Note, it may automatically start playing the sound for the lost AirPod.
If the area of your lost Airpod is quiet, you’ll hear it from 25 to 30 feet away, maybe more with sharp ears….. if it is quiet. If it was lost in a 24 hour casino or in a sawmill, your ear will need to be almost right next to it. This is also assuming it’s not under a folded towel or under a couch cushion that muffles the sound. Just as close to it as possible.
Get on this PDQ! I honestly don’t know how long out of the case an Airpod will keep juice in the battery. I’d assume this, this is ‘Mission Impossible:Airpod’, your mission gives ??? say 48 hours. Once the battery in that AirPods is dead your mission is over. That AirPod will only be found by old school FindMy (seeing it with your eyes).
One last suggestion, if you don’t find it with playing sound. It may be worth playing a sound every hour 5 or 6 times. Then call establishments around right AirPod last location. Maybe someone heard it and dropped it off at lost and found at the business it was found in.
Best of luck.