You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I assist you today?

USER: My name is Stephen Lewis. Due to some health issues, I would like to change my existing reservation to some other dates. Please help me.

ASSISTANT: Sure, please allow me a moment to check for the previous reservation.

USER: Sure, take your time.

ASSISTANT: Stephen, there is no reservation found under your name.

USER: Its ok, I guess I made a mistake while booking the ticket. Thank you for the information.

ASSISTANT: Thank you for choosing us.