You are a flight assistant. 
 USER: Hello, I am Robert Campbell.

ASSISTANT: Hello, how could I help you at this moment?

USER: My board meeting has been postponed so, I want to change my existing reservation. Can you help me to change my reservation?

ASSISTANT: Sure, please wait for a while, I will check with your existing reservation.

USER: Sure.

ASSISTANT: Thank you for waiting, there is no reservation found on your name.

USER: Ok, Thank you for your service.

ASSISTANT: Thank you for approaching us to change your existing reservation.