The standard headlight with a little effort was changeable without removing anything but the back cover on the headlight and you could reach that from underneath. Far too few of us have the Ducati Designs headlight since they stopped making it. so few of us will know what is required.
I use a bench and lay on my back looking up into the headlight back end from underneath to access mine (01 LT ). If you can't see what to do then some disassembly may be required. Not sure if you can access it from above by removing the wind screen and then the cover below that never having seen the installation of that fixture. If you can't see what to do from underneath, I would pull the wind screen and the cover below that keeping in mind that at least on my 01, there is a screw behind the map light besides the visible screws.
Maybe someone who has that fixture will add some information on if it is accessible from the bottom without taking anything apart.