Kibana how to filter out values of custom fields

Elastic Stack Kibana
5

Here is the config file for filebeat. I am basically mapping the fields from the json to the same field in fillebeat.

filebeat.prospectors:
- type: log
  enabled: true
  paths:
    - /log/*.log  
  multiline.pattern: '^{'
  multiline.negate: true
  multiline.match: after
  processors:
     - decode_json_fields:
         fields: ["timestamp", "message", "level"]
         process_array: false
         max_depth: 1
         target: ""
         overwrite_keys: true