Adding Backsplash
To add a backsplash you follow the same steps from adding edges. Click the option to the left of the grid that says backsplash and add it to the shape.
Changing Backsplash from Panel
You can then change the type of backsplash on the panel to the right like you did with.
Deleting Backsplash
Edges or you can delete it there as well.