You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I want to change my existing reservation, which I have reserved a month back. Can you please help me in changing my existing reservation?

ASSISTANT: Sure, I will help you.

USER: Thank you for the response.

ASSISTANT: Can I know your name please?

USER: My name is John Hernandez.

ASSISTANT: John, sorry to inform you that there is no active reservation found with your name in our records.

USER: It might have not booked properly while booking. It is not a problem. Anyways, thank you for the information.

ASSISTANT: Most welcome.