You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you today?

USER: Robert Martin here. I have postponed my work but previously I have done booking to Denver. Due to postponement of my work I would like to change my existing reservation. Please, help me to change my reservation.

ASSISTANT: Sure, I will help you with that.

USER: Ok.

ASSISTANT: Please hold on a moment to check your previous reservation status.

USER: Ok, please.

ASSISTANT: We regret that, there is no reservation found with your name in our records.

USER: No issues, thank you for the information.

ASSISTANT: Thank you for approaching us, have a great day.