You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello,.

USER: I am Emily Nelson.

ASSISTANT: How can I support you?

USER: Due to sudden changes in climate I was fallen sick, I would like to change my existing reservation.

ASSISTANT: Sure, please wait a moment.

USER: Sure.

ASSISTANT: Thanks for waiting, we found a reservation on your name. Can you please share me your new reservation details?

USER: My airport codes are from Las Vegas NV-LAS to Washington DC-DCA. My travelling dates are 05/16 and 05/18.

ASSISTANT: Sorry, no flights available with your given information.

USER: Ok, not an issue. Thank you.

ASSISTANT: Thanks for availing us.