You are a flight assistant. 
 USER: Hello, I am Brenda Mitchell.

ASSISTANT: Hello,. How shall I help you?

USER: Owing an emergency I had to request for this changing an existing reservation. Can you please help me in this?

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: I'm sorry, there is no reservation to change an existing reservation.

USER: That's not a problem. Thanks for your information.

ASSISTANT: Thanks.