How can I find the owner of a airtag

If you place this AirTag near your iPhone, or vice versa, AND the owner provided their contact information (phone number and/or email address) it would appear on your phone. That would be the only possible means to contact them. No one here, nor Apple can assist with this.

Ref: What to do if you find an AirTag - Apple Support

you can't really but if it has power and it within reach of an iphone with bluetooth enabled and an active internet connection the owner would be notified

apple would not legally be able to track customers who purchase equipment from them even if for people to be able to return said equipment to them

these are the tools they leave customers

Mark an AirTag or other item as lost in Find My on iPhone - Apple Support