You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I am very happy to change my existing reservation because my examination was postponed, now I have much time to prepare for the exam.So please help me in modifying my recent reservation.

ASSISTANT: Sure, please help me with your name to check your reservation details.

USER: Please check with the name Sandra Hall.

ASSISTANT: Sorry, no reservation is found on your name.

USER: It's ok. Thank you for the information.

ASSISTANT: Thank you for choosing us, have a nice day.