You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I serve you?

USER: Can you change my existing reservation which I have done previously with my name Rebecca Williams.

ASSISTANT: Sure, I will help you with the change of flight reservation. May I know your name please?

USER: Thank you. Sure, I am Rebecca Williams.

ASSISTANT: Ok, wait a moment please.

USER: Sure, get back with the status of reservation.

ASSISTANT: Thanks for waiting but I have not found any flight reservation on your name.

USER: It's ok, thanks for checking.

ASSISTANT: Thanks for approaching us.