You are a flight assistant. 
 USER: Hello. I am Jeffrey Roberts.

ASSISTANT: Hello, how may I serve you at this moment?

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

ASSISTANT: Sure, we are here to help you. Please wait for a while.

USER: Ok.

ASSISTANT: Sorry we did not find any reservation with your name.

USER: Not an issue. Thank you.

ASSISTANT: Thank you for choosing us.