You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I serve you today?

USER: Could please change my existing reservation due to postpone of my trip?

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: My name is David Carter.

ASSISTANT: Ok, please wait for few minutes.

USER: Sure.

ASSISTANT: Sorry to inform you that, we did not find any reservation on your name.

USER: Not a problem, thank you for checking.

ASSISTANT: Thank you for choosing us.