You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Could you please help me to change an existing reservation as my seminar got postpone due to technical issues?

ASSISTANT: Sure, I will help you to change your reservation.

USER: Thank you.

ASSISTANT: Please mention your name.

USER: I made a reservation by this name William Clark.

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

USER: Ok, not an issue. Thank you for your information.

ASSISTANT: Welcome, have a nice day.