You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, How can I best serve you today?

USER: Due to sudden change in my trip to another location, I would like to do some changes in existing my reservation. Can you please help me out?

ASSISTANT: Sure, I am here to help you with that, can I know your good name to proceed further?

USER: Charles Johnson here.

ASSISTANT:  I am very sorry to inform you that there is no reservation found under your name in our database.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for choosing us.