You can delete your WWWveilig Authenticator demo account and all its data at any time. Deleting removes your name, e-mail address, password hash, sign-in history and your phone's pairing at once; the audit log keeps only "account #n deleted" for up to a year.
Go to your account page and use Delete account at the bottom.
Enter the account's e-mail address. We send a link; opening it and confirming deletes the account.
In the WWWveilig Authenticator app you can also remove the account from your phone: Settings → the account → Remove.