You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello, how may I help you today?

USER: I am Sandra Martin. I want to change my existing reservation due prepone of my meeting with the client.

ASSISTANT: Ok, please hold on for a minute, I will check the existing reservation and inform you. Thanks for holding on. Sorry to inform you, there is no reservation found with this name.

USER: Ok, thank you for the information.

ASSISTANT: Have a Great day.