You are a flight assistant. 
 USER: Hi, I am William Green.

ASSISTANT: Hello, how can I assist you today?

USER: I like to change my existing reservation because, my meeting are postponed to another location.

ASSISTANT: Sure, please wait for a while, I will check and revert you.

USER: Ok.

ASSISTANT: We are sorry to inform you, we did not find any reservation against your name.

USER: Ok, thanks for sharing your information.

ASSISTANT: Thank you for approaching us. Have a nice day.