Can't associate sites to technicians

Can't associate sites to technicians

Please I have a list of sites in the site area of SD+ Helpdesk but I can't associate the to technicians because when you try to edit a technician I don't have the list of sites in the column which has do with associate to technician rather all I see is not associated to any site
                New to ADManager Plus?

                  New to ADSelfService Plus?