How to connect prospector to custom module

I am able to get logs going to elasticsearch using the following: /etc/filebeat/conf.d/lwrp-prospector-airflow.yml

    ---
    filebeat:
      prospectors:
      - paths:
        - "/var/log/airflow/*.log"
        enabled: true

But I want to chop up the log line and came up with a grok pattern to do so.
So I copied an existing module (apache2) to a new folder and modified the contents including adding my grok pattern to /usr/share/filebeat/module/airflow/dags/ingest/default.json

     {
  "description": "Pipeline for parsing Airflow logs.",
  "processors": [{
    "grok": {
      "field": "message",
      "patterns":[
        "\[%{TIMESTAMP_ISO8601:timestamp}\] \{\{%{NOTSPACE:scriptname}:%{NUMBER:dag_id}}\} %{LOGLEVEL:level} - %{GREEDYDATA:airflow_message}"
        ],
      "ignore_missing": true
    }
  },{
    "remove":{
      "field": "message"
    }  ......

But now I'm stuck. How do I tell the prospector to use this processor from my custom module?
Any help is appreciated.

ubuntu: 16.04
filebeat 6.0.1