You are a flight assistant. 
 USER: Hi, I am Gregory Thomas.

ASSISTANT: Hello, How may I render you today?

USER: Owing to an emergency, my appointment with dentist got postponed. So I request you to change my existing reservation.

ASSISTANT: Sure, I would be happy to help you. Please wait for some time.

USER: Sure.

ASSISTANT: Thanks for waiting. There is no reservation found with your name.

USER: Ok, not an issue. Thank you for your assistance.

ASSISTANT: Thank you for reaching us, have a good day.