To access Riffstation and its features, you will first need to create a new Fender Connect account. Fender Connect is your account for all Fender web sites and mobile apps, including Riffstation-iOS and Riffstation-Web. Provided you sign up with the same email address as the one linked with your old Riffstation account, your songbook will be automatically transferred over to your new account.
If you originally signed up to Riffstation via social media, you will have been asked to provide an email address. You must use that email address when signing up to Fender Connect for your songbook to carry over.