A forgotten password can be reset using the "Forgot your password?" link on the login dialog.
A prerequisite for receiving a password reset link is that an email address must be set for the given user in their profile (Tools - Company Users - Login credentials):
If the user does not have an email address on file, please contact customer support at ABRA Flexi — we will reset your password.
Other users should contact their administrator, who can change their password in the Company Users module.