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.
how I can skip the entity node message which I am getting again and again for each run
An entity node must contain at least one character in the prompt message, so you cannot leave it blank. It is possible to designate the entity node as “hidden”. In this configuration, the node will capture a value from the previous utterance without prompting.
Thanks, I will try with this configuration.