You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I guide you?

USER: Can you help me to change my existing reservation?

ASSISTANT: Yes, can I know your name for changing reservation?

USER: Sure, my name is Melissa Nelson.

ASSISTANT: I'm sorry Melissa, there are no reservations with your name.

USER: Ok, thank you.

ASSISTANT: Thank you.