You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am David Lewis.

ASSISTANT: How can I assist you today?

USER: I need to change my recent reservation due to postpone of my bank exam. Could you please help me in doing that?

ASSISTANT: Sure, will you please give me a moment?

USER: Sure.

ASSISTANT: Thanks for waiting, there is no reservation found under your name.

USER: No problem, thank you for your information.

ASSISTANT: Welcome, have a great day.