Open Command Prompt as Administrator and run: DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs (Replace 'D' with your actual drive letter!)
If you want, I can produce a longer how-to guide with step-by-step commands for a specific Windows version—tell me which version (e.g., Windows 10 21H2, Windows 11) and whether you need a GUI or command-line walkthrough. microsoftwindowsnetfx3ondemandpackagecab extra free