how to sync airpods 3

Hello Maxim_Maslov,

Thanks for that info and for choosing the Apple Support Communities. If we understand correctly, you are having an issue with your AirPods. To help with this, please follow these steps:

1. "Put your AirPods in their charging case, and close the lid.

2. Wait 30 seconds.

3. Open the lid of your charging case, and put your AirPods in your ears.

4. Go to Settings > Bluetooth. Or go to Settings > [your AirPods].

* If your AirPods appear there as connected, tap the More Info button  next to your AirPods, tap Forget This Device, then tap again to confirm.

* If your AirPods don't appear there, continue to the next step. 

7. Put your AirPods in their charging case, and keep the lid open. 

8. Press and hold the setup button on the back of the case for about 15 seconds, until the status light on the front of the case flashes amber, then white.*

9.

10. Reconnect your AirPods: With your AirPods in their charging case and the lid open, place your AirPods close to your iPhone or iPad. Follow the steps on your device's screen.

AirPods can be associated with one Apple ID. If you want to use AirPods (3rd generation) or AirPods Pro (1st or 2nd generation) that someone else has used, they first need to remove the AirPods from their Apple ID."

And those steps are from How to reset your AirPods and AirPods Pro - Apple Support

Also, if you want to replace the lost AirPod, you can do that here: Choose Your Country or Region - Apple Support

Cheers!

If you lose the one airpod, removed the airpods from BT settings and add it again.

but airPods has a BT detection with out case, try to find it