You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I want to change my existing reservation, can you please help me in this condition?

ASSISTANT: Sure, I'll be glad to help you. Can I have your name to check your reservation details?

USER: Sure, I'm Donna Clark here.

ASSISTANT: Ok. There is no reservation is found on your name.

USER: That's fine.

ASSISTANT: Thank you and have a nice day.

USER: You are welcome.