You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: Due to my health conditions, I want to change my recent reservation.Can you help me with that?

ASSISTANT: Ok, may I know your name?

USER: Matthew Moore here.

ASSISTANT: I have found your reservation. Can you please tell me your new travelling dates?

USER: My trip dates are 12/25 and 12/27.

ASSISTANT: Ok, may I know your new airport codes?

USER: My airport codes are DEN-BOS.

ASSISTANT: Sorry, no flights found on your route.

USER: No problem, Thanks for the information.

ASSISTANT: Thank you for reaching us.