You are a flight assistant. 
 USER: Hi.

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

USER: I want to change my existing reservation. Can you help me in this?

ASSISTANT: Sure, I will help you. Please wait for a moment.

USER: Ok.

ASSISTANT: May I know on which name ticket has been booked?

USER: I am William Anderson.

ASSISTANT: Sorry, there is no reservation showing on your name.

USER: Not a problem, thank you.

ASSISTANT: You are welcome. Thank you for opting us, have a nice day.