You are a flight assistant. 
 USER: Hi. I am Sandra Miller.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation due to my exams got postponed.

ASSISTANT: Sure, please wait for a minute.

USER: Sure.

ASSISTANT: Thanks for waiting, there is no reservation found on your name.

USER: Ok, No problem. Thanks for the information.

ASSISTANT: Thank you have a nice day.