Letting go of the button is the drop part of drag and drop. For example, an icon of a file can be dragged and dropped onto the waste can icon for deletion or onto a printer icon for printing.

Drag and Drop icons Use Settings to configure the icon setting Use Control Panel. Here you can find the Other System Icons Tray section that you need to expand. It contains all the app icons that ...

Right-click the app and select "Get Info." In the window that pops up, you'll see a tiny icon in the upper left corner. Drag and drop the custom icon image on top of the icon in the left corner.