You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I assist you?

USER:  I want to change an existing reservation due to my meeting got preponed. Can you change my existing reservation?

ASSISTANT: Sure, may I know your name?

USER: Catherine Adams is my name.

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

USER: Ok, not an issue. Thank you for the quick response without delay.

ASSISTANT: Thank you for choosing us, have a nice day.