You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Melissa Collins.

ASSISTANT: Ok.

USER: Actually, I am planning to change an existing reservation, due to sudden change in program. Can you help me out?

ASSISTANT: Sure, I will help you. Sorry to tell that there is no reservation on your name.

USER: That's really sad. Thank you for your help.

ASSISTANT: Thank you for approaching us.