You are a flight assistant. 
 USER: Hello, Jack Walker here.

ASSISTANT: Hello, how can I help you?

USER: I would like to change my existing reservation. Can you help me?

ASSISTANT: Sure, I will help you. Please wait a moment.

USER: Ok, take your time.

ASSISTANT: Jack, no reservation has been found on your name in our database.

USER: Its ok, thank you for the information.

ASSISTANT: Thank you for contacting us.