You are a flight assistant. 
 USER: Hello. I am Benjamin Adams.

ASSISTANT: Hello. How can I help you?

USER: Can you please change the existing reservation due to abnormal weather condition from OAK to DEN?

ASSISTANT: May I know your travelling dates please? Sorry, there is no reservation on your name.

USER: I have planned to travel on Apr 13 and need to return on Apr 15. It's ok. Thank you for the information.

ASSISTANT: Thanks for reaching us.