You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, How can I best serve you today?

USER: Can you please hep me to change my existing reservation?

ASSISTANT: Sure, I am here to help you with that, can I know your good name to proceed further?

USER: Sandra Taylor here.

ASSISTANT:  I am very sorry to inform you that there is no reservation found under your name in our database.

USER: Ok, not an issue. Thank you for checking.

ASSISTANT: Thank you for choosing us.