making a new vhost.conf called helpdesk.teknerds.conf and adding this to that vhost.conf:
DocumentRoot /opt/otrs/bin/cgi-bin/
and adding this to the otrs.conf file which is in /etc/apache2/conf.d:
# agent, admin and customer frontend
Alias /otrs-web/ "/opt/otrs/var/httpd/htdocs/"
Alias / "/opt/otrs/bin/cgi-bin/"