You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Mark Jackson here.

ASSISTANT: How may I be of your assistance?

USER: Could you please help me in changing my existing reservation?

ASSISTANT: Sure, I'll try to help you in changing an existing reservation.

USER: Thank you.

ASSISTANT: Please wait a moment I'll check the reservation status.

USER: Sure.

ASSISTANT: Thank you for waiting, I am sorry to say you that there is no reservation found under your name in our database.

USER: Not a problem, thank you.

ASSISTANT: Thank you for approaching us.