How do I move my acount to another email service?

Hello, If you keep recieving that error, that means you have created a mozilla account with that email that you want to make secondary. If you want to be able to add the secondary email and set as primary, you first must delete the account associated with your other email, then add the email to your account. If you cannot access the account but can access that email, make sure to first recover the account, then delete it. Once deleted, you will most likely be able to add that email.