You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Can you please change my existing reservation?

ASSISTANT: Sure, may I know your name please?

USER: Sure, I am Charles Carter.

ASSISTANT: Ok, please wait for a while.

USER: Sure.

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

USER: Ok, not an issue. Thank you for your information.

ASSISTANT: Thank you for choosing us.