a) Press “Windows Logo” + “R” keys on the keyboard.
b) Type “appwiz.cpl” in the “Run” command box and press “ENTER”.
c) In the “Programs and Features” window, click on the link “Turn Windows features on or off”.
d) Check if the “.NET Framework 3.5 (includes .NET 2.0 and 3.0)” option is available in it.
e) If yes, then enable it and then click on “OK”.
f) Follow the on-screen instructions to complete the installation and restart the computer, if prompted.
This will install the .NET Framework 3.5 feature on the computer. There is also another way by which .NET Framework 3.5 gets installed on the computer. This is done by the apps on demand.
If an app requires the .NET Framework 3.5, but doesn't find that version enabled on your computer, it displays the prompt for installing the .NET Framework 3.5 on demand, either during installation, or when you run the app for the first time after its installation. In this prompt, you can choose the option “Install this feature” to enable the .NET Framework 3.5 on the computer."