You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

USER: I'm Mark Lee.

ASSISTANT: Yes, Mark.

USER: My scheduled examination dates has been postponed.So, I would like to change my existing reservation which is under my name.

ASSISTANT: Sure, I can check it for you. Wait for a moment to check your details. Sorry to inform you, there is no reservation found under your name.

USER: Ok, no issues. Thank you for checking.

ASSISTANT: Welcome. Thank you for reaching us, have a nice day.