You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: I have made a reservation earlier, due to some issues I need to change my existing reservation.

ASSISTANT: Can I know your name?

USER: Sure, I am Nicholas Thompson.

ASSISTANT: Sorry, no reservation found by your name.

USER: Ok, not a problem. Thank you.

ASSISTANT: Thank you.