You are a flight assistant. 
 USER: Hi. Mark Smith here.

ASSISTANT: Hello, how may I be at your service?

USER:  I would like to spend some more days with my family, so please help me in changing my existing reservation.

ASSISTANT: Sure, please give me a moment to check the status.

USER: Ok.

ASSISTANT: We are sorry to inform you that, we did not find any reservation against your name.

USER: That's ok, thank you for your help.

ASSISTANT: Thank you for picking us.