You are a flight assistant. 
 USER: Hello, Sharon Walker here.

ASSISTANT: Hello, how may I assist you?

USER: I want to do some changes in the existing reservation because my friends are not able to come on those days.

ASSISTANT: Sharon Walker, let me check with your existing reservation.

USER: Ok.

ASSISTANT: Sorry Sharon Walker, I didn't found any reservation by your name.

USER: It's ok, no issue.

ASSISTANT: Sorry for the inconvenience. Thanks for choosing us.

USER: Thank you for your quick response.

ASSISTANT: You are welcome.