Here is a medical discussion of this disorder, listing treatments and prognosis and other factors. You have to register to read the entire article; registration is free.
https://emedicine.medscape.com/article/1519417-overviewHere is a less-complete discussion of the subject, available free on MedlinePlus (a webpage from the U.S. National Library of Medicine).
https://www.mayoclinic.org/diseases-conditions/narcissistic-personality-disorder/symptoms-causes/syc-20366662?p=1disclaimer: I am retired reference librarian with special training in the field of medical literature. I am not a physician and cannot recommend treatments; I just find info from reputable sources. What you do with this material is up to you.