You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: Brenda Green here. I would like to change my existing flight reservation that has been booked earlier this week. Could you please help me in re-modifying my dates in the reservation?

ASSISTANT: I am here to help you about that Green.

USER: Thank you.

ASSISTANT: Give me a while to find an existing reservation under your name.

USER: Sure, take your own time to check the reservation.

ASSISTANT: Sorry Green, I have checked all my booking list but I am not able to find any existing reservations under your name.

USER: That's fine, thanks for you help and information.

ASSISTANT: You are most welcome, thank you for choosing our service.