On your floor plan or when in 3D, select Draw>Symbol>Exterior and select from the available corbels or if you have Softplan+, you can go in Manufacturer>Softplan+>Osborne Wood Products>Corbels and brackets for a larger selection. In 3D you can more easily position the height of your corbel.
To speed things up also, when selecting Symbols, you can enter Corbel in the Search box at the bottom and it will provide you with the different choices.
If you don't want your corbel to show on the floor plan, you can out them on a layer that you can turn off.