When you are in the Navigation window, you can click the right mouse button over a corner between adjacent walls. In the context menu you will find the command Corner->Tile shower-box corner (if you can’t see it, it means that you did not click over the corner). This will lead you to the mask you can see in the next image.
Here you can decide which tile to apply to the tiled corner. Left and right areas (layer) can be identical or different: it’s up to you and generally it depends on the shower-tray size. Once you confirm this choice you will get back to the Navigation window and see the result. If something’s wrong, you can easily UNDO ( Ctrl + Z ) and repeat the operation.
This article is valid for DomuS3D® 2017 and later versions