You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you today?

USER: I would like to change my existing reservation, can you please help me out?

ASSISTANT: Sure, I am here to help you. May I know your name please?

USER: My name is Steven Collins.

ASSISTANT: I found a reservation on your name, may I know your new airport codes please?

USER: My airport codes are DTW to DEN.

ASSISTANT: Ok, can you please provide your travelling dates?

USER: My planned travel dates are on Jan 15 and Jan 17.

ASSISTANT: Ok, do you have any specifications?

USER: I prefer an economy class.

ASSISTANT: Sorry Steven Collins, there are no flights available on your requested dates.

USER: Ok, no issues. Thank you for your information.

ASSISTANT: Welcome, thank you for choosing us. Have a great day.