You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I am Mary Lewis. Due to my health problem I want to change my reservation, can you please help me that?

ASSISTANT: Ok, let me check with your existing reservation. Sorry to inform you, there is no reservation found under your name.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for reaching  us, have a great day ahead.