How can I see the emails used on my old phone? or used in Apple ID for registration.

I need to find out the email address for a fortnite account that I forgot. Therefore, they suggested that I write to the support service and ask them to help me view the emails used for registration or something else. Here's the message from Fortnite support that referred me to you: Look, I've never owned an iPhone myself, but I know they have a few different security features, including the ability to spoof email. Perhaps this is exactly the situation you have, and this letter is to the state prosecutor’s Fortnite account.”