You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you today?

USER: My friend has changed the tour plan to other day, can you help me in changing existing reservation?

ASSISTANT: Sure, I am here to assist you about that cancellation.

USER: Thank you.

ASSISTANT: For to check that reservation I need your name, please provide me?

USER: Previously, I have reserved my ticket with the name of Donna Baker.

ASSISTANT: There is no previous reservation done on your name, so, there is no ticket found to cancel it.

USER: Ok, may be there is a mistake during booking the ticket. Thank you for providing information.

ASSISTANT: Don't know exactly, but do not have any information about that. Thanks for contacting us, have a great day.