When updating the assets list, you provide it with the latest information about the assets it shows.
To update the assets list:
Open a building. For more information on how to do so, see section 4.6.1., 5.4.3. or 6.1.1.
Go to the building card (see image below).
Click the tab called "Assets" (see image below). Within the tab called "Assets" you will find a assets list. In the assets list you will see the assets associated with the building you are working with.
Click "Update list" (see the first image below). When you do so, the assets list will be updated (see the second image below).