How to find 3rd gen. airpod without the find my setting . I never set it up when I purchased

The only way to track an Apple device is through find my.

Apple does not track users devices, you can’t use a serial number or receipt to track anything.

From the following article, which you should carefully read:

Find your lost AirPods - Apple Support

”Find My is the only way that you can track or locate a lost or missing device.”