Authelia provides a workflow to let users reset their password when they lose it. To disable reset password functionality please see the configuration docs.
A simple click on
Reset password? for starting the process. Note that resetting a password requires a new identity verification using the e-mail of the user.
Give your username and receive an e-mail to verify your identity.
Once your identity has been verified, fill in the form to reset your password.
Now you can authenticate with your new credentials.