OK so i'm assuming he wasn't banned etc and has just forgotten his password etc.
As I understand it he's probably fucked until the problem with new registrations is sorted as Admin can't send out confirmation link e-mails for new accounts or password reminders etc.
I'm saying this based on Admin making a comment to this effect when some people who had the same username and passwords for UKP and UKE were changing their passwords after UKE went into meltdown