You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I provide assistance to you?

USER: Can you please change my existing reservation?

ASSISTANT: Sure, we are here to help you. Please share your name to check your reservation status.

USER: Sure, I am David Brown.

ASSISTANT: Please wait a minute.

USER: Sure.

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

USER: Ok, not an issue. Thank you for your information.

ASSISTANT: Thank you for choosing us.