If you have forgotten your password, click on "Passwort vergessen?" in the login area. You can find the login area for the productive system at: https://app.billwerk.com/#/login and for the sandbox at https://sandbox.billwerk.com/#/login.
The following confirmation is displayed if the email address has been entered correctly:
Follow the link and choose a new strong password. The strength of your password is displayed below the input. If possible, use letters, numbers and special characters to generate a particularly strong password. The longer a password is, the more secure it is. Finally, click on "Speichern" and log in to billwerk.
If you want to change your password, go to "Settings > Account > Change Password" in billwerk and enter your current and new password. There you will see the strength of the new password. Select the strongest password possible and click on "Save".