Email already associated with another account
I have a Apple Id "abc" associated with abc@gmail.com. When I login to apple using my apple id, I am able successfully login. After login, it says the Apple id is not in the correct format, use your email address. I give abc@gmail.com, it says email already associated with another account.
Please give a different email ID.
How to resolve this issue?
[Re-Titled by Moderator]