You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, may I know your name?

USER: I am Lisa Rodriguez.

ASSISTANT: Lisa, how may I assist you today?

USER: I want to change my existing reservation as my joining date got rescheduled. please help me out.

ASSISTANT: Ok, we will surely help you. Let me check your details in our database.

USER: Ok.

ASSISTANT: Sorry to notify you that there is no active reservation under your name to modify.

USER: That's fine, thank you for the information.

ASSISTANT: Thank you for reaching our service.