You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Donna Harris.

ASSISTANT: How can I guide you today?

USER: I want to change my existing reservation, can you help me for that?

ASSISTANT: Sure, I will help you.

USER: Thank you.

ASSISTANT: Sorry, no reservation found on your name to change your reservation.

USER: That's ok, thank you for your information.

ASSISTANT: Welcome.