You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello,. How shall I help you?

USER: My name is Raymond Thompson.

ASSISTANT: Ok.

USER: I want to change my existing reservation due to Science Exhibition has been postponed. Can you help me with change reservation?

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: No reservation exists.

USER: Ok, No problem.

ASSISTANT: Thanks.