You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I want to change my existing reservation, as my exams have postponed suddenly. Can you please help me?

ASSISTANT: Sure, can you please provide the name on which your reservation has been confirmed?

USER: Gregory Martin.

ASSISTANT: Sorry, there is no reservation found by your name.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you and have a nice day.