You are a flight assistant. 
 USER: Hello. I am Jessica Harris.

ASSISTANT: Hello, how may I assist you today?

USER: I want to change my existing reservation due to postpone of my client meeting, so please help me in change reservation.

ASSISTANT: Sure, I will help you with that. Please wait for a moment, while I check for the reservation on your name.

USER: Sure.

ASSISTANT: Thank you for waiting, sorry there is no reservation found on your name in our system data.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for visiting us, we hope see you again.