First and really important is that you must own access to the old email. This doesn’t see to be the case here.
Without you can not change the email address. You must be able to receive the first email on the old address. Then you can go to next step.
The email is now marked as taken in the system and waits for the owner to get changed as new address for the account.You have to wait ~48 hours before you can repeat the process.
