You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you?

USER: I need to change my existing reservation owing to an emergency.

ASSISTANT: May I know your name?

USER: My name is Ryan Collins.

ASSISTANT: We found your reservation, may I know your new airport codes?

USER: Airport codes are DCA and DFW.

ASSISTANT: May I know your travelling dates?

USER: Travelling dates are Sept, 18 and Sept, 20.

ASSISTANT: Is there any connection limit?

USER: I prefer connecting flight.

ASSISTANT: Do you have any class preferences?

USER: I prefer business class ticket.

ASSISTANT: Is there any airline preference?

USER: I prefer to fly in a normal-cost airline.

ASSISTANT: May I know any other specifications you require?

USER: I would like to return in the afternoon.

ASSISTANT: Sorry, there are no flights found with your required dates to travel.

USER: Thank you.