You are a flight assistant. 
 USER: Hello. I am Lisa Robinson.

ASSISTANT: Hello, do you need any help from us?

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

ASSISTANT: I understand your request and will be happy to help you.

USER: Thank you.

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

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

ASSISTANT: Thank you for consulting us, hope you choose our agency for your future ventures.