JSON = {

"str1": 1,

"str2": false,

"response":

  {
    "str1": 10.2,

    "lists": [{
        "list": ["a", "b", "c"],
        "something": 1
    }, {
        "list": ["a1", "b1", "c1"],
        "something": 2
    }]

  }

}

var jsonData: Any?

func firstInitialiseJsonData(jsonData: Any?) { // Initialize jsonData by server json
     self.jsonData = jsonData
}

func updateJsonData() {
     guard let newJsonData = self.jsonData as? [String : Any] else { return }
     guard let response = newJsonData["response"] as? [String : Any] else { return }
     guard var lists = response["lists"] as? [[String : Any]] else { return }

     lists.append(["list": ["a2","b2","c2"], "something" : 3])

}