This is a paid asset, but now you can download 3D Tilemap Free.
Detail this asset from Unity Store: Original Link
3D Tilemap v1.1 (Latest version)
“If possible, please buy the package to support the developer”
The 3D Tilemap Package helps you create levels easily in your projects. It allows you to place objects or “Tiles” in your scene just by clicking. It also includes a special “Self Tiling Floor” that will automatically change its appearance based on its neighbours.
As an added feature, the 3D Tilemap Package allows you to “Bake” the levels you create, combining them into a single mesh, which you can save in your assets.