You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Mark Clark.

ASSISTANT: How can I serve you today?

USER: I want to change my existing reservation due to postpone of my exams, can you help me with that?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Please wait.

USER: Sure.

ASSISTANT: Sorry, no reservation found under your name to change.

USER: No problem, thank you for the information.

ASSISTANT: Thank you for opting us.