You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Brian Davis.

ASSISTANT: How may I aid you?

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

ASSISTANT: Sure, I am gleeful to help you.

USER: Thank you.

ASSISTANT: Sorry, there are no reservation found on your name.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for choosing us.