E-MAIL ID ISSUE @ ''ICLOUD.COM''

How can I retrieve Apple ID that is used through 'icloud.com'?

My friend created an iCloud e-mail (example***@icloud.com); not ***@yahoo, ***@gmail.com, or any other but, ***@icloud.com.

Now to recover the password - Apple is accepting to send the password to the @icloud e-mail, which we don't have access to it. But we have access to the yahoo e-mail that her customer might used in converting to icloud.com.

How can I recover this ***@icloud.com e-mail address? Your help is highly needed here.

Thanks.