[otrs] Editing customer details?

I sent the following recently and then got a message saying I was not subscribed! Odd. Anyway I have resubscribed and here is the email. Hi, when a user mails in for the first time and creates a ticket that fine. How do I then edit this customers details? I've added some custom fields which work fine normally. I want to retrieve this customer via their email and then add to these fields. Doing a search in [customer user management] on their email shows no results. thanks Mike