Unblocking a person allows them to call you and send messages again, but it does automatically add them back to your Facebook friends list or send them a notification. Unblocking via Mobile App (Android/iOS) Open the Messenger app.

I notice you're asking about unblocking someone on Messenger, but your message ends with "make a long paper" — I think there might have been a typo or a mix-up.

No. Facebook does not send a notification to the other person when you unblock them. They will only realize it if they search for your profile and find that it is visible again, or if they try to message you and it goes through.