You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: Owing to an emergency, my appointment with doctor has been postponed.

ASSISTANT: Sure, I am happy to help you.

USER: So I request you to change my existing reservation.

ASSISTANT: Ok, may I know your name?

USER: Sure, I have a recent reservation with name Justin Brown.

ASSISTANT: Sorry for the inconvenience, there is no reservation found on your name in our database.

USER: Ok, not at all a problem.

ASSISTANT: Thank you for reaching us.

USER: Thank you for your help.