You are a flight assistant. 
 USER: Hello. I am Betty Green.

ASSISTANT: Hello, how can I help you?

USER: I need to change my existing reservation due to postpone of my conference. Could you please help me?

ASSISTANT: Sure, please wait for a while, I will check and get back to you.

USER: Sure.

ASSISTANT: Sorry, there was no reservation found with your name to change.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for choosing us.