1. Create New index with correct mapping 

    PUT /INDEX_COPY
{
    "mappings" : {
        "properties" : {            
    "id": {
      "type": "keyword",
      "ignore_above": 256
    },
    "actor": {
      "properties": {
        "group": {
          "type": "keyword",
          "ignore_above": 256
        },
        "id": {
          "type": "keyword",
          "ignore_above": 256
        },
        "name": {
          "type": "keyword",
          "ignore_above": 256
        }
      }
    },
    "description": {
      "type": "text"
    },
    "app": {
      "properties": {
        "build": {
          "type": "keyword",
          "ignore_above": 256
        },
        "name": {
          "type": "keyword",
          "ignore_above": 256
        },
        "server": {
          "type": "keyword",
          "ignore_above": 256
        },
        "stage": {
          "type": "keyword",
          "ignore_above": 256
        },
        "version": {
          "type": "keyword",
          "ignore_above": 256
        }
      }
    },
    "entity": {
      "properties": {
        "group": {
          "type": "keyword",
          "ignore_above": 256
        },
        "id": {
          "type": "keyword",
          "ignore_above": 256
        },
        "name": {
          "type": "keyword",
          "ignore_above": 256
        }
      }
    },
    "changes": {
      "type": "nested",
      "properties": {
        "name": {
          "type": "keyword",
          "ignore_above": 256
        },
        "created": {
          "type": "date",
          "format": "yyyy-MM-dd HH:mm:ss||yyyy-MM-dd"
        },
        "ip": {
          "type": "keyword",
          "ignore_above": 256
        },
        "groupId":
          {
            "type": "keyword",
            "ignore_above": 256
          },
        "groupName": {
          "type": "keyword",
          "ignore_above": 256
        },
        "newValue": {
          "type": "text",
          "fields": {
            "keyword": {
              "type": "keyword",
              "ignore_above": 256
            }
          }
        },
        "oldValue": {
          "type": "text",
          "fields": {
            "keyword": {
              "type": "keyword",
              "ignore_above": 256
            }
          }
        }
      }
    },
    "request": {
      "properties": {
        "ip": {
          "type": "keyword",
          "ignore_above": 256
        },
        "timestamp": {
          "type": "date"
        }
      }
    }
        }
    }
}

  2. Move data from old index to copy 

    POST _reindex
{
  "source": {
    "index": "INDEX_NAME"
  },
  "dest": {
    "index": "INDEX_COPY"
  }
}

  3. Remove old index

    DELETE /INDEX_NAME

  4. Assign original index name as alias to new index with correct mapping 

    POST /_aliases
{
    "actions" : [
        { "add" : { "index" : "INDEX_COPY", "alias" : "INDEX_NAME" } }
    ]
}