You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello,.

USER: I am Nancy Anderson.

ASSISTANT: Do you require any assistance?

USER: I need to change my recent reservation due to postpone of my sister marriage to some other date. Could you please help me in doing that?

ASSISTANT: I'm sorry, no reservation exists by name Nancy Anderson.

USER: No problem, thank you for your information.

ASSISTANT: Have a nice day!.