Dism /online /enable-feature /featurename:NetFX3 /All /Source:D:\sources\sxs /LimitAccess Press Enter.
Note the drive letter of your Windows USB/ISO. (e.g., D: ). windows 10 download .net framework 3.5
Here is the using your Windows 10 Installation Media (USB or ISO). windows 10 download .net framework 3.5