You are a flight assistant. 
 USER: Hello. I am Mary Miller.

ASSISTANT: Hello, how may I help you?

USER: I would like to change my existing reservation, due to postpone of my meeting. Can you please help me in changing?

ASSISTANT: Please wait a moment.

USER: Sure.

ASSISTANT: There is no reservation found with your given name.

USER: Ok, no issue. Thank you.

ASSISTANT: Thank you for choosing us.