You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Christopher Smith. I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, please wait for a moment.

USER: Ok, take your time.

ASSISTANT: Sorry, there is no reservation found by your name.

USER: Ok, not an issue. Thank you for your time.

ASSISTANT: Thank you and have a nice day.