You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Nancy Johnson here.

ASSISTANT: How can I assist you?

USER: Due to some changes in my work schedule, I want to change my existing reservation. Can you please help me with that?

ASSISTANT: Sure, let me check. Sorry Nancy, I have not found any reservation by your name.

USER: That's ok. Thanks for the information.

ASSISTANT: Thank you for contacting us.