Assuming we're just talking about an account you forgot the email and password for, or never linked it to Kabam, submit a ticket to Kabam support, then go through the identity gauntlet. You'll need the estimated creation date, the dates and amounts of two purchases, and other identifying information to prove you own the account. If you pass the test, then they can help you from there.
Where can I submit a ticket to Kabam support?
My original account wasn't linked to Kabam.