The Terrain Settings Copier Asset is a special asset that is used to selectively copy settings from the Terrain component, Terrain Data asset, and Terrian Collider component from the source terrain(s) to their slices.
This asset is used to comply with different versions of Unity, as each version has different settings that can be copied.
By default, the Asset is included with the package and you do not need to worry about it. The only instance where you need to concern yourself with it is if you have accidently deleted the asset or moved it from its default location.
The asset is stored in the Assets/Editor Default Resources/Deep Space Labs/TerraSlicer/ScriptableAssets folder. If you delete it or move it outside of this folder, you will need to move it back to this folder, or regenerate the asset using the menu command (see below)
To recreate/regenerate the asset, use the command located on the top Unity menu bar. Just choose Assets - > Deep Space Labs -> Terra Slicer -> Regenerate Terrain Settings Copier.