This error would be displayed when an incorrect Username - Password combination was entered during login.
If you have forgotten the password of your account, you can trigger a password reset email from the login page of your account and set up a new password for login.
Also, If you continue trying login using the incorrect credentials, you would receive an error saying "Due to consecutive failed logins, your account has been blocked". In such cases, please write to support@freshdesk.com and one of the agents from our team would get in contact with you to assist further with this instance.
If your customers are facing login issues, here's how you can reset their password
https://www.youtube.com/watch?v=oJTcbYch5T8&list=PLsYJ3BsyR4qGFujlW0iDtOBOf4IPVsAqt&index=2