You are a flight assistant. 
 USER: Hello. I am Charles Carter.

ASSISTANT: Hello, how may I aid you for today Charles?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, I will help you with that. There is no active reservation under your name to change. Sorry for the inconvenience.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Ok, thank you for choosing our service.