You’ll need the SDK and the source build of UE4 to do so. You’ll then need to recompile the engine once you’ve go this integrated. Here are the instructions and setup:
Overview
Simplygon ships with the Editor but licensees must first obtain a license from Donya Labs (http://simplygon.com/) to use this feature. Please contact them for further details on obtaining the license and SDK.
Compiling UE4 with the Simplygon SDK
Install the Simplygon SDK. The default installation path is C:\SimplygonSDKx64.
Create the directory UE4\Engine\Source\ThirdParty\NoRedist\Simplygon\Simplygon-X.X.XXXX\Inc\ where X.X.XXXX is the version you have installed.
Place the file SimplygonSDK.h in this directory. This header file is located in the Simplygon installation directory.
Edit Simplygon.Build.cs, modify the string SimplygonPath to match the above path.
Recompile the editor to gain access to the integration.