You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Donald Harris.

ASSISTANT: How can I help you?

USER: I want to change my existing reservation, as my  engagement has postponed. Can you please help me out?

ASSISTANT: Sure, I am here to help you. Sorry Harris, there is no reservation found with your name.

USER: That's ok. Thank you for your information.

ASSISTANT: You are welcome.