Haasi

Hello, a few years back luckkaz traded me his Onix to evolve it but I didnt know that it will be locked inside my storage since I was not in Sinnoh before. It just came back to my mind that I still have it. Can we transfer it back to him somehow? I would appreaciate it. I feel bad for still having it and not being able to give it back since its an abosolute monster regarding its stats. BR, Jakob