You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you today?

USER: My name is Samuel Lee, I want to change my existing reservation due to postpone of my friend engagement.

ASSISTANT: Sure, I am ready to help you. Please hold on.

USER: Sure.

ASSISTANT: Thanks for waiting. Sorry, we found there is no reservation with your specification.

USER: No problem, thank you for your quick response.

ASSISTANT: Thank you for choosing us, have a nice day.