You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you today?

USER: Can you help me to change my recent reservation because my trip dates are got postponed?

ASSISTANT: May I know your name to proceed further?

USER: I am David Lewis.

ASSISTANT:  I am very sorry to inform you that there is no reservation found under your name in our database.

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

ASSISTANT: Thank you for choosing us.