You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Mark Clark. I need to change my existing reservation. Can you please help me out?

ASSISTANT: Sure, please wait for a moment.

USER: OK.

ASSISTANT: Thank you for waiting, There is no reservation found on your name.

USER: OK. No issue. Thank you for the information.

ASSISTANT: Thank you for reaching us.