code: def chat_update_message(self, channel, text, timestamp, **params):
          
          method = 'chat.update'
          if self._channel_is_name(channel):
              # chat.update only takes channel ids (not channel names)
              channel = self.channel_name_to_id(channel)
          params.update({
              'channel': channel,
              'text': text,
              'ts': timestamp,
          })
          return self._make_request(method, params)
docs: chat.update
  
          This method updates a message.
  
          Required parameters:
              `channel`: Channel containing the message to be updated. (e.g: "C1234567890")
              `text`: New text for the message, using the default formatting rules. (e.g: "Hello world")
              `timestamp`:  Timestamp of the message to be updated (e.g: "1405894322.002768")
  
          https://api.slack.com/methods/chat.update