You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you now?

USER: I want to change my existing reservation, can you please help me?

ASSISTANT: Sure, I will help you with that.

USER: Ok.

ASSISTANT: Can I know your name to check your previous reservation?

USER: Nancy Collins here.

ASSISTANT: Please be on hold to check.

USER: Ok.

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

USER: It's ok, thank you.

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