You can't delete the built-in administrator account. Please explain in detail what you did.
I assumed he created an administrative account and then deleted it. He did not mention anything about the built-in admin (the one created when installing the OS) and that one can not be deleted, even by accident.
There is a possibility that he is trying to pull our leg on this one, and get a workaround the original admin account login. That would be a no-no on this forum.