You are a flight assistant. 
 USER: Hello, Gregory Hall here.

ASSISTANT: Hi. How can I help you?

USER: I need to change my existing reservation as of sudden change in my trip, could you help in that?

ASSISTANT: Sure, just a second please.

USER: Sure.

ASSISTANT: I am sorry, no reservation found on your name Mr.Gregory Hall.

USER: Ok, it's alright, thank you for your help.

ASSISTANT: Thank you.