You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you today?

USER: I am Charles Hall. Due to my health problem I want to change my active reservation, can you please help me to change my reservation?

ASSISTANT: Sure, I am here to help you.

USER: Thank you.

ASSISTANT: Sorry Hall, there is no reservation found as per your name to change it.

USER: Ok, no problem. Thank you.

ASSISTANT: You are welcome.