First of all,you to need to have windows cd or image file of the windows you have installed .Insert it into your pc or laptop or any other devices.
Then,open the cd or image file
Open Sources folder,there you see sxs folder
Copy the sxs folder
Paste it in the next location but I preferred it to Drive c:/.
Now ,Open command prompt as admin
And put the command
Dism /online /enable-feature /featurename:netfx3 /all /source:c:sxs /limitaccess
After that,you will get a message ‘Operation completed successfully’
If again you face error then
Comment for any errors.