Hi Sana,
Below are the steps -
1. Create On Ready event in screen.
2. Add below Javascript in ready event.
var scriptNode = document.createElement('script');
scriptNode.src='https://www.gstatic.com/dialogflow-console/fast/messenger/bootstrap.js?v=1';
document.head.appendChild(scriptNode);

3. On screen create df-messenger html tag using HTML Element widget.

4. Messenger available on browser.
