Microsoft released KB4524101 for NETFramework 4.8 and 3.5 FOR Windows 10 1809 on the patch Tuesday 08 October 2019. This update was previously rolled out in the Cumulative Update that’s dated September 24, 2019.
The knowledge base for 4515871 of the patch for .NET Framework4.8 and 3.5 for Windows 10 1903 and 1909 (KB4515871) is the description of this patch. Microsoft is releasing all the packages speedily today.
KB4524101 NET Framework 4.8, 3.5 Windows 10 1909
In order to get 08 Oct 2019 cumulative update for NET Framework 4.8, 3.5 Windows 10 1909 go to Settings > Update & Security > Windows update and click on “Check for updates”.
In case you want to install the Standalone package for the same navigate to Microsoft update catalog, match the architecture of your device and click on Download. Once a popup appears, select the link there.
Source – Knowledge base