You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, Please inform me how can I best assist you now?

USER: I would like to change my existing reservation, can you help me in doing that?

ASSISTANT: Sure, I can help you in that.

USER: Thank you.

ASSISTANT: May I know your good name please?

USER: I am Sarah Walker.

ASSISTANT: Ok, Please allow me a moment to check for the previous reservation in our database.

USER: Sure, take your time.

ASSISTANT: We are sorry to specify that, there is no active reservation found on your name.

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

ASSISTANT: Thanks for choosing us, wish you a nice day.