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

ASSISTANT: Hello, how may I be of your helping hand today?

USER: I want to change my existing reservation due to postpone of my conference.

ASSISTANT: Sure, we are here to help you. Please wait for few minutes.

USER: Sure.

ASSISTANT: Sorry to inform you that, we could not find any reservation on your name.

USER: Not an issue, thank you.

ASSISTANT: Thank you for choosing us. Have a good day.