You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Mark white. I want to change my existing reservation due to my health issue. Can you help me out?

ASSISTANT: Sure, please wait a minute.

USER: Sure.

ASSISTANT: Thank you for your time. Unfortunately we didn't found any reservation by your name.

USER: Ok, No problem. Thank you.

ASSISTANT: Thank you for picking us.