You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I want to change my existing reservation due to postpone of my exams. Can you help me in that?

ASSISTANT: Ok, may I know your name?

USER: Sharon Nelson here.

ASSISTANT: I am very apologetic to tell you, there is no active reservation by your name.

USER: Ok, no problem. Thank you for checking.

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