You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I guide you?

USER: I am Alexander Hill. I would like to change my existing flight ticket. Could you please help?

ASSISTANT: Sure, can I know your preferable dates?

USER: Sure, take your time.

ASSISTANT: I am sorry, there are no reservations with your name.

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

ASSISTANT: Thank you, have a good day.