He would need to delete the cookies, as they are stored on his computer(s).
What I would suggest doing is to become him, then change the password manually, then give him the new password.
In the past, I have found the temporary one does not work for some reason and by manually altering it the user was able to log in.
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Fans Focus - Focusing on Fans of Sport
(Okay - mainly football (the British variety
at the moment - but expanding all the time....))