You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you?

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

ASSISTANT: Ok, could I have your name please?

USER: I am Melissa King.

ASSISTANT: Ok, please allow me a moment.

USER: Sure.

ASSISTANT: Sorry, there is no reservation with your name in our portal to make changes further.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: You are welcome, have a great day.