You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Larry Allen. I want to do some changes in the existing reservation because my friends are not able to come on the those dates, can you please help me?

ASSISTANT: Sure, wait for a minute. Ok, may I know your new airport codes?

USER: Sure. My airport codes are OAK to DEN.

ASSISTANT: Ok, can I have your preferable dates?

USER: My travelling dates are 12/01 to 12/03.

ASSISTANT: Sure, wait for a minute.

USER: Sure.

ASSISTANT: Sorry, no flight's found on your details.

USER: That's fine. Thank you for your service.

ASSISTANT: Thank you for contacting us.