You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: I am Charles Johnson. I am planning to change an existing reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Sure, please wait for a moment.

USER: Sure.

ASSISTANT:  Sorry, no active reservation found on your name in our data base.

USER: That's fine, thank you for your service.

ASSISTANT: Welcome, thank you for reaching us.