You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, may I know how best I can help you today?

USER: I am Kenneth Brown. I want to change my existing reservation due to postpone of my exams, can you help me with that?

ASSISTANT: Sure, We are ecstatic to help you.

USER: Thank you.

ASSISTANT: Please give me a moment.

USER: Sure.

ASSISTANT: Thank you for waiting, but I am sorry to say that, there is no active reservation found with your name in our database to change it.

USER: That's ok, no problem. Thank you for the information.

ASSISTANT: Thank you for choosing us.