You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello,. How may I serve you?

USER: I am Karen Taylor, I just want to change my existing reservation.

ASSISTANT: OK,  please wait for a while I will check with the status and revert you.

USER: OK.

ASSISTANT: Sorry, there is no reservation found on your name. Thank you for choosing our service.

USER: Thank you.