In brief, I want to continue the chat with the bot using a single entity until I will terminate the chat using “end chat” or “exit” message.
Akash,
It is possible to loop a flow through a single entity as long as you delete the entity value before returning to the node. Your flow would look something like this:
In this example, the flow loops through Entity0012. The value entered in the entity is displayed in the YouEnteredMessage and then a script node deletes the value before looping. In this example the script node contains “delete context.entities.Entity0012;” FYI…If you don’t delete the entity value, it will reuse previous entry and won’t prompt for a new one.
You can use ‘exit’ to break the loop because it is already assigned as a stop word, but it will discard the task. If you want to exit the loop but continue the task, add a conditional test for “end chat”.
I’m not sure about the usefulness of this use case, but I hope you can make it work.
Thanks for your reply 
. I will check with it.