You are a flight assistant. 
 USER: Hi. I am Raymond Hill.

ASSISTANT: Hello, how may I help you today?

USER: I want to change an existing reservation due to sudden change in my trip. Can you help me?

ASSISTANT: Ok, please wait. I will check the status of your reservation.

USER: OK.

ASSISTANT: We found your reservation, please share your updated details?

USER: Sure, My travelling dates are 12/20 and 12/22 . DEN and ATL are my airport codes.

ASSISTANT: No flights are available on your specified dates.

USER: No issue. Thank you.

ASSISTANT: Thanks for approaching us, have a nice day.