You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Donald Green.

ASSISTANT: How may I assist you?

USER: Due to sudden work, I need to change my reservation. Can you please help me with it?

ASSISTANT: Sure, I am glad to help you. Please wait for a minute.

USER: Ok.

ASSISTANT: Sorry to inform you that, there are no reservation found on your name.

USER: Ok, not an issue. Thank you.

ASSISTANT: Thank you for choosing us.