You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I aid you?

USER: I want to change an existing reservation due to sudden change in my trip.

ASSISTANT: Give me a moment, let me check your details.

USER: Ok.

ASSISTANT: May I know your name please?

USER: I am Rebecca Davis.

ASSISTANT: Sorry Davis, I didn't found any reservation basis on your details.

USER: No issue. Thank you for your response.

ASSISTANT: Most welcome.