It obviously didn't work. Nothing changed, right?
BUT... If he were able to go back in time and "change" things for you, one argument goes that your "current" timeline (as you now know it) will continue as though nothing had happened, but he would have created a new offshoot (vestigial) timeline that will cause a differnt future -- a future that your "current you" can not know about! So, asking him to change the past for you won't help you at all, and it won't "prove" that his machine really works!
...just a thought!