You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I am Andrew Williams. I want to change my existing reservation due to postponed of brother marriage.

ASSISTANT: Wait for a while.

USER: Can you please help me with that?

ASSISTANT: Sorry to say, there is no reservation found under your name to change it.

USER: Not an issue. Thanks for your information.

ASSISTANT: Thank you for choosing us.