You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you today?

USER: I am Alexander Green want to change my existing reservation due to postpone of my meeting with Tom Cruez.

ASSISTANT: Sure, please wait a moment I will check and get back to you. Sorry to notify you that there is no reservation found on your name.

USER: Ok, thank you.

ASSISTANT: Thanks for choosing us.