how can you find a iCloud locked iPhone owner

I have a iPhone 5 that I had replaced the logic board as mine was damaged. I got the logic board on eBay, it was suppose to be with AT&T & iCloud unlocked. I could't get pass the start up page, it always was asking for the right carrier SIM. That was a year ago. I recently found out it is a T- mobile iCloud locked logic board. I need to contact the original person it is iCloud locked too, and hopeful get them to unlock it. any ides? T- Mobile was't any help.