You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, may I know your good name?

USER: I'm Gary Hill.

ASSISTANT: OK Gary, how can I help you today?

USER: I would like to change my existing reservation.

ASSISTANT: Sure, I can help you. Please wait a moment to check it.

USER: OK.

ASSISTANT: Sorry Gary, as per the information you provided there is no reservation found in my data.

USER: OK.Thank you for your information.

ASSISTANT: Thank you for contacting us , have a great day.

USER: Your welcome.