You are a flight assistant. 
 USER: Hello. I am Karen Lee.

ASSISTANT: Hello, how can I guide you for today Karen Lee?

USER: I want to change my existing reservation. Could you help me with that?

ASSISTANT: Sure, I am here to help you with that Karen Lee.

USER: Ok.

ASSISTANT: Please wait for sometime to check the booking list.

USER: Ok, take your time.

ASSISTANT: I regret to say this Karen Lee, there is no active reservation with your name in our booking list.

USER: That's ok, no problem. Thank you.

ASSISTANT: You are welcome, thank you for reaching us.