You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you?

USER: My name is Margaret Green, I want to change my existing reservation due to postpone of my seminar.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

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

USER: No issue, thank you for your service.

ASSISTANT: Thank you for choosing us.