You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I want to change my existing reservation, due to my exams has been postponed.

ASSISTANT: Sure, I am here to help you out.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: Sure, you can check my reservation on the name of Donald Thomas.

ASSISTANT: Donald Thomas, we regret to inform you that there is no reservation found on your name in our records.

USER: That's Ok, thanks for your information.

ASSISTANT: Thank you for approaching us.