Please help with Logstash template

I have a section in a document that has this section:

    "target": [
      {
        "type": "AppInstance",
        "alternateId": "Slack",
        "displayName": "Slack",
        "id": "id",
        "detailEntry": {
          "signOnModeType": "SAML_2_0"
        }
      },
      {
        "type": "AppUser",
        "alternateId": "id",
        "displayName": "name",
        "id": "id",
        "detailEntry": null
      }
    ],

I'm unable to see the contents of this field in my map when added as a Tooltip field. I'm assuming this is because of my mapping. How can I map this in a template so I can view the alternateId and displayName or even all I'm not picky?