You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you today?

USER: I want to do some changes in my existing reservation. Can you help me for that?

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

USER: My name is Catherine Johnson.

ASSISTANT: Sorry Catherine Johnson, there are no flights reserved on your given name formerly.

USER: That's ok, thank you for checking.

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

USER: Welcome.