You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Kimberly Walker here.

ASSISTANT: how can I abet you today?

USER: I want to change my existing reservation which I have done in the past.

ASSISTANT: Sure, I will help you. Please hold on for a while.

USER: Ok.

ASSISTANT: Sorry Walker, no reservation found with your name to change your reservation.

USER: It's ok, anyway thank you for the help.

ASSISTANT: Thank you for contacting us.