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 with this?

ASSISTANT: Can you please tell the name on which the reservation has been confirmed?

USER: Yes, I have booked the ticket on Gary Miller.

ASSISTANT: Sorry, there is no reservation found on the name had you have provided.

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

ASSISTANT: Thank you and have a nice day.