The inductor logstash-forwarder agent is installed as part of the inductor setup . For more details on inductor setup refer, build-install-configure-an-inductor document. Retrieve the logstash cert from any of the ES nodes and update it at this path /logstash-forwarder/cert/logstash-forwarder.crt
Once the cert is updated restart the inductor logstash agent via the command inductor restart_logstash_agent cloud-name.