when the user is interacting with the bot and when bot does not have answer to reply the chat bot should automatically connect to live agent and live agent should start conversation with the user. So I thought of doing it with flown where the love agent gets message on teams channel but in this how live agent should join conversation with user instead of chat bot. Only the message is getting in teams channel .So another way is building own engagement hub but how to do this is not available in the Microsoft documents.So can you please help me in connecting to live agent in PVA
As described in this article you can hand off to a live agent by using 'Escalate' under Go to another topic.
Use hand-off to live agent - Power Virtual Agents | Microsoft Docs