You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Myself Karen Green.

ASSISTANT: Karen Green, how may I assist you today?

USER: I need to change my existing reservation due to my exams got postponed, can you please help me?

ASSISTANT: Yes, I will help you.

USER: Thank you for your kind response.

ASSISTANT: I have found your details, please help me with your planned travel dates.

USER: My new travelling dates are May,01 and May,03.

ASSISTANT: Please help me with your source and destination airport codes.

USER: My news airport codes are LAS and MSP.

ASSISTANT: Please help me with your preferred class to fly.

USER: I need an economy class in my booking.

ASSISTANT: Ok, do you need a direct or connecting flight?

USER: I need a direct flight for my travel.

ASSISTANT: Please let me know with your departure and return time.

USER: My depart time should be in the afternoon.

ASSISTANT: Do you have any other preferences with respect to your journey?

USER: That's enough for my reservation.

ASSISTANT: Please allow me a minute.

USER: Sure.

ASSISTANT: Karen Green, I am really sorry to inform you that there are no active flights available for your journey.

USER: That's ok, thank you very much for searching the flights.

ASSISTANT: Thank you for reaching us. Have a great time.