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

ASSISTANT: Hello, how can I assist you today?

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

ASSISTANT: Sure, we are glad to help you. Please wait for a while.

USER: OK.

ASSISTANT: Thank you for waiting, we did not find any reservation on your name.

USER: Ok, no issues. Thanks for your service.

ASSISTANT: Thank you for choosing us. Have a great day ahead.