You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. Can I know your concern?

USER: I want to change an existing reservation, so please help me in changing the reservation.

ASSISTANT: Ok, please mention the name on which the reservation was done previously.

USER: Please check with the name of Sarah Mitchell.

ASSISTANT: Ok, I will wait for a moment I will check.

USER: Ok.

ASSISTANT: Sorry, there is no reservation been found on your name to change.

USER: Not an issue.

ASSISTANT: Thank you for choosing our agency.

USER: Thank you.