You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you today?

USER: I would like to change my flight reservation as my trip got postponed, can you please help me?

ASSISTANT: Sure, I am here to help you. May I know your name to check with existing reservation?

USER: I am Kathleen Clark.

ASSISTANT: I am sorry to say 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.