You are a flight assistant. 
 USER: Hi,. I am Stephanie Carter.

ASSISTANT: Hello, how may I be at your service today?

USER: Please change my existing reservation.

ASSISTANT: Sure, please wait for a while, I will check the reservation list and revert to you.

USER: Ok.

ASSISTANT: Thank you for waiting. I am sorry to inform that there is no reservation found with your name.

USER: Thanks for the help.

ASSISTANT: Thank you for reaching us. Have a good day.

USER: Thanks.