You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you today?

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

ASSISTANT: Sure, I am here to help you. May I know on whose name the ticket has been reserved formerly?

USER: Barbara Walker.

ASSISTANT: Ok, hold on for a moment. Let me check.

USER: Ok.

ASSISTANT: Sorry Barbara Walker, there are no flights reserved on your given name formerly.

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

ASSISTANT: Welcome, thank you for choosing us. Have a great day.