You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I guide you?

USER: I am Dennis Jackson.

ASSISTANT: Ok.

USER: Due to my health problem I want to change my reservation, can you please help me in that?

ASSISTANT: Sure, please hold on for a moment, let me check.

USER: Ok, I will wait.

ASSISTANT: I am sorry, there are no reservations with your name. Thank you.

USER: Ok, no problem. Thank you.