You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, Can I know your name?

USER: My name is Thomas Hill.

ASSISTANT: How can I serve you?

USER: I want to change my existing reservation due to postpone of my exam.

ASSISTANT: Ok, let me check the details of your existing reservation.

USER: Ok.

ASSISTANT: Thanks for your time, there is no reservation found with your name.

USER: No problem, thanks for your service.

ASSISTANT: Thank you for reaching us.