I have a fortnite account which I don't know what the Gmail I had used but the username is...

Hi there! My name is Darhyl and I’d be more than happy to help you with your query.

I'm sorry you are experiencing this with your Fortnite account.

To answer your inquiry according to the official Epic Games website: https://www.epicgames.com/help/en-US/c-Category_EpicAccount/c-AccountSecurity/i-don-t-remember-the-email-on-my-epic-games-account-a000089084

"If you can't remember what email address you have linked with your Epic Games account, there are a few things that you can do to remember it.

If you are logged into your account, you can go to your Account Management page by going to https://www.epicgames.com/account/personal/. There you can see an obfuscated version of your current email address.

If you are unable to log into your account, you can use our self-service flow to help you find your email. Click here to start: Search for your account email:

https://www.epicgames.com/help/en-US/wizards/w5

Note: Make sure you are not currently logged into any Epic Games account.
The way it works is:

You will need to tell us either your Epic Display name, Account ID, or the Display name of your connected account (could be console or social account).
We will search for a matching account.

If we find an account, we will send a message to the account's email address so that you know which is the email associated with your Epic Games account.

Note: You'll need to have access to that email address to see our response.

Alternative options that you could try:

Check your browser's settings to see if you have saved your email and password for your Epic Games accounts.
If you have any connected accounts such as consoles or social platforms, you can try to use them to access your Epic Games account."

Note/Disclaimer: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.

Thank you for your kindness and understanding! Please feel free to let me know if you need anything else.

Best Regards,
Darhyl

Hi there! This is Ronnie, an independent advisor.

Nice to meet you and I hope you are having a great day!

I understand you need help on your account problem.

Sorry to hear about what happened there, email is really important for us to recover the account and if you forget that, you may also try retrieving your log in email using an alternate email or phone through this link:

https://account.live.com/username/recover

Just a heads up, it will be very difficult to get the log in information if you only know the gamertag because what is important there is your email address that you use for that account.

it would be really Help full hope u can help me to recover my old hotmail

so the issue is they changed the email used to sign into the account as well, microsoft still shows it linked to his gmail when i use the "i dont know my username" feature, but it tells me his gmail is linked to an unknown email

What about you know the username and the gmail ?