You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I would like to change my flight reservation as I met with an accident, can you please help me?

ASSISTANT: May I know your name?

USER: My name is Nancy Baker.

ASSISTANT: Sure, please wait a minute.

USER: Sure.

ASSISTANT: We have found your reservation. Can I know your airport codes?

USER: Sure, I would like to travel from LAX to DEN.

ASSISTANT: Please provide your trip dates.

USER: I want to depart on Jan 4th and return back on Jan 6th.

ASSISTANT: Ok, please wait a minute.

USER: I prefer for an business class.

ASSISTANT: Sorry, there is no flight available.

USER: Sad to hear that, thank you for checking.

ASSISTANT: Most welcome.