An error message like the one pictured above means that we already have an account on file with the email address being submitted. Try logging into your preexisting account. If you don't recall what your password is, click "set new password" next to the "Log In" button to have a password reset email sent to you.
Please note that BrainHQ requires that each user have their own separate account with their own separate email address. There isn't a feature to support multiple people training with one email address.