You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, do you need any help from us?

USER: Christopher Smith here. I need to change my existing reservation, can you help me in doing that?

ASSISTANT: Sure, please allow me a moment.

USER: Sure.

ASSISTANT: Sorry, there is no reservation with your name in our portal to make changes.

USER: Ok, no issues. Thank you for the information.

ASSISTANT: You are welcome, have a great day.