I buy one of mystery box and i got an ipad but the i pad still linked to a previous owner's account. I want to return that ipad but I don’t know how to contact to the owner that iPad

Forget it and just recycle that device responsibly.

You'll never find its owner.

Best of Luck to You!`

Since you cannot post personal information here, the chances of that person actually signing up here asking about a missing iPad of the exact type and model are slim to none.

Also, because sharing of personal information is not allowed here, either, no one can here can post phone numbers, email addresses or location addresses for you to be able to send this iPad to!

Most users only sign up here for Apple device/product troubleshooting purposes.

These Apple support communities are NOT an Apple device Lost and Found.

You are just wasting your efforts here with that device.

If you are this concerned about getting this device back to its rightful owner, hand this iPad over to the “local” police or local regional police for them to try and locate that iPad's owner.

You will have little to no luck here.

Sorry.