You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I want to change my existing reservation.Will you please help me?

ASSISTANT: OK, may I know your name please?

USER: My name is Stephanie Scott.

ASSISTANT: Sorry Scott, unfortunately there is no reservation found under your name in our database.

USER: Oh! OK,no problem. Thank you.

ASSISTANT: Thank you, have a good day.