You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Sandra Hill here.

ASSISTANT: Can you please tell me how can I assist you?

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

ASSISTANT: Ok, please wait for a while. Sorry, no reservation found on your name.

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

ASSISTANT: Most welcome.