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

ASSISTANT: Hello, how may I help you at this moment? Sure. Please wait for a while. I will check.

USER: Due to an emergency, I would like to change my existing reservation.

ASSISTANT: Ok. Sorry, there is no reservation found on your name.

USER: That's ok, thank you for checking.

ASSISTANT: Welcome. Thank you for reaching us.

USER: Welcome.