You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, what can I do for you today?

USER: I need to change my existing reservation, Can you please help me with that?

ASSISTANT: Yes, I am here to help you. May I know your good name to check with your previous booking?

USER: Sarah hall.

ASSISTANT: Ok, Sarah Hall. Please allow me to check with your booking status for a moment.

USER: Sure.

ASSISTANT: I regret to inform you, there is no reservation in our data base by your name.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for reaching us, have a great day.