You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: I want to change my existing reservation due to  postpone of my exams, so can you help me with this?

ASSISTANT: Sure, I will help you to change your reservation.

USER: Thank you.

ASSISTANT: Can you please share your name?

USER: My name is Joseph Miller.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: Thanks for your time, we regret to inform you that there is no active reservation found on your name.

USER: Not a problem, thank you for checking.

ASSISTANT: Thank you for availing us.