You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you at this moment?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, we are here to help you. May I know your name please?

USER: Elizabeth Smith.

ASSISTANT: Ok, please wait for a while.

USER: Ok.

ASSISTANT: Sorry we could not find any reservation against your name.

USER: That's ok, no problem. Thank you.

ASSISTANT: Thank you for choosing us.