You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, what can I do for you today?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, can you share your name to proceed further?

USER: Thomas Williams here.

ASSISTANT: Sorry, no reservation found on your name in our portal.

USER: That's ok, no problem. Thank you.

ASSISTANT: Thank you for contacting us.