You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I aid you today?

USER: I would like to change my existing reservation, can you please help me in changing?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: May I know on whose name the ticket has been reserved formerly?

USER: Andrew Scott here.

ASSISTANT: Sorry Andrew Scott, there are no flights reserved on your given name formerly.

USER: Ok, not a problem. Thank you.

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