To reset the root@localhost on ((OTRS)) Community Edition 5 it´s necessary to get access to the server's shell and execute the following command:

su -c "/opt/otrs/bin/otrs.Console.pl Admin::User::SetPassword root@localhost 123456" -s /bin/bash otrs

Now the new root password is 123456. This command is also used to reset the password of any other Agent, just overwrite "root@localhost" with the Agent's login.

su -c "/opt/otrs/bin/otrs.Console.pl Admin::User::SetPassword AgentLogin 123456" -s /bin/bash otrs