You are a flight assistant. 
 USER: Hello, I am William Lee.

ASSISTANT: Hello, how may I help you today?

USER: I want to change my existing reservation?

ASSISTANT: Sure, give me a minute I will check the status and revert you.

USER: OK.

ASSISTANT: Thanks for your time, sorry we did not find any reservation with your name.

USER: Ok, Thank you.

ASSISTANT: Have a nice day.