You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I be at your service today?

USER: Can you please help me to change my existing reservation?

ASSISTANT: Sure, may I know your name please?

USER: Sure, I am Joshua Campbell.

ASSISTANT:   Sorry, there is no reservation matching with your name in our portal to make changes further.

USER: Ok, not an issue. Thank you for checking.