You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you today?

USER: I want to change my existing reservation due to sudden postpone of my trip dates. Can you help me with that?

ASSISTANT: Sure, I will try to help you but I need your name to proceed further?

USER: Thank you. Kevin Mitchell here.

ASSISTANT: Sorry to tell you that, there is no active reservation found with your name in our database to change it.

USER: Ok, no problem. Thank you for your assistance.

ASSISTANT: My pleasure.