You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation as my trip dates has been postponed. Can you help me with that?

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

USER: Thank you. I am Mary Hall.

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

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

ASSISTANT: You are welcome and have a nice day.