You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you today?

USER: Can you please help me to change my existing reservation, due to exams has been postponed?

ASSISTANT: Sure, may I know your name?

USER: Sure, my name is Lisa Hernandez.

ASSISTANT: Please wait a moment, let me check with the previous reservation status.

USER: Sure.

ASSISTANT: Sorry, there are no active reservations on your name to change.

USER: Ok, thank you.

ASSISTANT: Thank you for reaching our service.