You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you today?

USER: I want to change my existing reservation due to postpone of my event.

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

USER: Sure, I am Robert Evans.

ASSISTANT: Ok, please wait for a minute.

USER: Sure.

ASSISTANT: We found a reservation on your name, can you please help me with your journey dates?

USER: My travelling dates are Aug 2 and Aug 4.

ASSISTANT: Ok, let me know your airport codes.

USER: Sure, my airport codes are EWR and SEA.

ASSISTANT: Is there any other concerns to say?

USER: Yes, I prefer to travel in a economy class.

ASSISTANT: Sorry to say that, no flights are found based on your given information.

USER: No worries, thank you for the information.

ASSISTANT: Thank you for choosing us.