You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I assist you for the day?

USER: I am David Green. Due to postpone of my meeting, I would like to change my existing reservation. Can you please help me in changing?

ASSISTANT: Sure, I am here to help you with that reservation change. Please wait for a moment.

USER: Sure.

ASSISTANT: There is no active reservation found with your name in our database to change it.

USER: Ok, no problem.

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

USER: Thank you.