You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Is it possible to change my existing reservation as I have modified my trip?

ASSISTANT: May I know your Name please?

USER: My name is Gregory Evans.

ASSISTANT: Give me a moment.

USER: Sure.

ASSISTANT: Sorry, no reservation found.

USER: Never mind, thank you for checking it.

ASSISTANT: Thank you for choosing us.