You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you today?

USER: My name is Mathew Williams and I would like change an existing reservation.

ASSISTANT: Sure, let me check your reservation details in our database.

USER: Sure.

ASSISTANT: Sorry, we couldn't found any reservation on your name.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for choosing us.