To update the drivers you have to go to the official nvdia website and with the app you will be able to update your drivers, and to use direct 11 here is the link to epic’s web site
https://www.epicgames.com/help/en-US/c-Category_Fortnite/c-Fortnite_TechnicalSupport/how-do-i-force-fortnite-to-use-directx-11-a000085695