You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

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

ASSISTANT: Sure, I am here to help you out. May I know your travelling dates please?

USER: I prefer to travel on Aug 15 and Aug 17.

ASSISTANT: Wait a moment please, let me check your reservation with your name. Steven Thompson, 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 time.

ASSISTANT: Thank you for choosing us.