You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I serve you today?

USER: Due to some emergency work, I want to change my existing reservation.

ASSISTANT: May I know your name please?

USER: I am Margaret Brown.

ASSISTANT: Thank you for providing name.

USER: Will you help me in this ticket booking?

ASSISTANT: Unfortunately, there are no reservation found.

USER: Ok, thank you for your information.

ASSISTANT: Thank you for choosing us.