You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you now?

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

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

USER: I am Michael Thomas.

ASSISTANT: Please be on hold.

USER: Sure.

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

USER: Ok, no problem. Thank you for your information.

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