You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you now?

USER: I want to change my existing reservation, my music concert got postponed. Can you please help me out with that?

ASSISTANT: Sure, I am glad to help you with that. Can I know your name to check your previous reservation?

USER: My previous reservation was booked with name Mark Roberts.

ASSISTANT: Please wait a moment to check.

USER: Ok, I will wait.

ASSISTANT: We regret to inform you that, there is no reservation found on your name in our records.

USER: Ok, thank you for checking.

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