You dont need to compile engine or plugin from source. Just do the following:
Enable volumetrics plugin and restart editor.
In content browser, click View Options at bottom right, and make sure ‘show engine content’ and ‘show plugin content’ are ticked.
Now click root folder in top bar of content browser.
Scroll down and choose ‘Volumetrics Content’
Now you can navigate to some sample maps and load them. For example: Volumetric Content/Tools/VoxelizeMeshes/Maps/VoxelizeTestmap_StaticMesh