First, add any decoration that will be easier to do while the tiers are separate, such as adding ribbon to the bottom or decorating the sides. Then, using a sharp knife, cut three to five pieces of plastic dowel rod to the height of your frosted tier. Arrange these in a circle in the center of the cake to provide support for the tier that will go on top of it.
Once the marzipan is draped over the cake, gently pull down the sides to cover any gaps. Smooth the flat of your hand down the sides, pressing the marzipan to the cake and amoothing out any creases or overlaps, Rub the flat of your hand or a cake smoother over the top firmly to flatten and smooth the surface. Smooth out the sides in the same way. Trim off any excess marzipan around the bottom of the cake with a sharp knife and peel it off the board. This can be kept in an airtight bag or container for use next time.