I wanna help a person back to the reality, what can i do?

Go to a therapist.: As a friend, there is nothing you can do other than help them see a professional. Even if you were a well trained therapist, you would not have the objectivity to be of real assistance. If severe, take them to a psychiatric emergency service or er.

Reality lessons?: You should try and speak in person with your friends family and close friends. If someone loses touch with reality, it is difficult to reason with them. Enlisting the families help will increase chances for success to get your friend to agree for help.