You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, do you need any help from us?

USER: Can you please help me in changing my existing reservation?

ASSISTANT: Sure, could I have your name please?

USER: My previous reservation has done with the name Deborah Thompson.

ASSISTANT: Ok, please allow me a moment.

USER: Sure, take your own time.

ASSISTANT: I have found your reservation, can you please tell me your trip dates?

USER: My preferable journey dates are Dec 18 and Dec 20.

ASSISTANT: Ok, could you please share your origin and destination airport codes?

USER: My airport codes of journey are IAH and DTW.

ASSISTANT: Ok, please allow me a moment.

USER: Sure.

ASSISTANT: Sorry, there is no flight on your requested travelling dates.

USER: Ok, not an issue. Thank you for providing information.

ASSISTANT: You are welcome, have a great day.