If you are in doubt whether you have created an account to sync your data between devices, you can attempt to log in. If you receive an alert saying there is no user with this identifier, then you most certainly don’t have an account. Please refer to this article to create one.
However, just in case you actually input an old password, and you are certain you do have an account, please attempt to reset your password. You will find the instructions here.
If the email field vibrates after tapping the Reset password button, then it means there is no user with this email address in the system, therefore you definitely don’t have an account 🙂