You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: I am Donald Clark. I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, please wait a moment.

USER: Ok.

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

USER: That's ok, no problem. Thank you.

ASSISTANT: Thank you for approaching us.