You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Christopher Nelson here.

ASSISTANT: How can I assist you at this moment?

USER: I need to change my existing reservation, can you help me in doing that?

ASSISTANT: Sure, I will help you with this. Please give me a moment to check your reservation status.

USER: Sure, take your time. Ok, not an issue.

ASSISTANT: Christopher Nelson, there is no active reservation found under your name in our database.

USER: Thank you for the information.

ASSISTANT: Thank you for contacting us.