You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you for today?

USER: I am Sarah White. I am planning to change an existing reservation because of some  urgent work at office.Can you please help me out to change reservation?

ASSISTANT: Yes, I will try for best assistance. Hold on for a second, I will check for your previous reservation.

USER: That's really great, take your own time.

ASSISTANT: Sorry to inform you that there is no reservation found on on your name in our database. Anything else I can help you with?

USER: No, I don't have any other plans.

ASSISTANT: Thank you for reaching us.

USER: Thank you for your service.

ASSISTANT: Feel free to reach us anytime.

USER: That's fine.