How do I increment my count field of my document from logstash?

Elastic Stack Elasticsearch
1

I want to update one field of my document/log in elasticsearch from logstash.

My logstash conf file

input { 
	http {
    host => "127.0.0.1" # default: 0.0.0.0
    port => 31311 # default: 8080
  }
}

output { 
  stdout { codec => json },
  elasticsearch {
  		action => "update"
  		bind_host => "127.0.0.1"
  		bind_port => 9200
  		document_id => "ET00009682"
  		index => "in12"
  		type => "event"
  }
}

I want to increment my count field by one how do I specify that in my output of logstash.

Note: I know to update i need to use this script

"script" : "ctx._source.count += 1"

but I am not sure where to place it in output of logstash?

Kindly help
thanks