You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Melissa Lee.

ASSISTANT: How can I assist you today?

USER: I want to do some changes in my existing reservation. Can you help me for that?

ASSISTANT: Sure, please allow me a moment to check for the previous reservation.

USER: Sure, take your time.

ASSISTANT: I found your reservation. Can you please help me with the airport codes?

USER: My travelling airport code are from DFW to LAS.

ASSISTANT: Could you please help me with the travel dates?

USER: My travelling dates are June 05 and June 07.

ASSISTANT: May I know your connection limit?

USER: I need a single connecting flight.

ASSISTANT: Do you have any class preference?

USER: I prefer economy class.

ASSISTANT: Do you have any other specification that you are looking for?

USER: My airline preference is normal cost.

ASSISTANT: Melissa Lee, I am sorry to inform you that there is no flight available at your request.

USER: That's ok, thank you for checking.

ASSISTANT: You are welcome. Thank you for reaching us.