Hello Tomas, thanks for answering.
After following your instructions, I was able to delete indices through the graylog: DataNodes/API : Proxy direct access to Data Node’s API
In addition to that, I was also able to use CURL command to communicate directly with the following command:
curl -X DELETE --key key_datanode.crt --cert cert_datanode.crt --cacert ca_datanode.crt "https://<redacted>:9200/unifi_1" --pass <redacted>
{"acknowledged":true}
Much appreciated for your time and support on this.