By working your way down the navigation tree structure, make sure the supplement object you wish to open is visible in the navigation tree (see image below).
Click the supplement object you wish to open (see the first image below). Note that the supplement object you click will open. When a supplement object opens so does its object card (see the second image below). Via the object card you can work with a supplement object. For more information about supplement objects, see section 8.3.in the manual for Buildings. You will find it here.
