You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you today?

USER: I am Steven Lewis. I would like to change my existing reservation, due to examination schedule postponed. Can you please help me?

ASSISTANT: Sure, I am here to help you. Please stand by.

USER: Ok, I will wait for your response.

ASSISTANT: Thanks for waiting, we found a reservation on your name. Please specify your travelling dates?

USER: My travelling dates are 03/27 and 03/29.

ASSISTANT: Help me with your airport codes?

USER: My airport codes are DEN and EWR.

ASSISTANT: Thanks for your details, there is no flight found on your desired routes.

USER: That's ok, no problem. Thank you for checking.

ASSISTANT: Thank you for reaching us.