You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you at this moment?

USER: Actually, I want to change my existing reservation due to postpone of my exam can you please help me in this intent?

ASSISTANT: Sure, I will help you with that. Can I have the name on which ticket has reserved earlier?

USER: Sure, my name is Timothy Mitchell here.

ASSISTANT: Ok Timothy, please wait a moment.

USER: Sure, take your own time.

ASSISTANT: Thank you for waiting.

USER: My pleasure.

ASSISTANT: Sorry Timothy, there is no reservation found under your name to change.

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

ASSISTANT: My pleasure. Thank you for choosing us.

USER: Welcome.