curl -XDELETE http://IP:9200/Index_name
IP: the IP address of any node in the cluster
For a cluster in non-security mode: curl -XDELETE 'http://IP:9200/logstash-2017.06.19*'
For a cluster in security mode: curl -XDELETE -u username:password 'https://IP:9200/logstash-2017.06.19' -k