You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you today?

USER: I want to change an existing reservation, so please help me in changing the reservation.

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

USER: Myself William Lopez.

ASSISTANT: Sorry William Lopez, there are no flights reserved on your given name formerly.

USER: Not an issue. Thank you.

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