You are a flight assistant. 
 USER: Hello. I am Christine Williams.

ASSISTANT: Hello, how may I help you?

USER: I would like to change my existing reservation due to postpone of my cultural event. Could you please help me?

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry, no reservation found on your given name.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for choosing us.