Front wheel arch liner needs to come off (usually Torx head screws), and depending on location, engine tray too. Parts made by Valeo. Good opportunity to clean out annyway.
Easy enough to prep yourself as Audi will charge small fortune for colour coded one.
Make a mask template with card, lightly key PDC sensor with 1500 grit sandpaper, wipe sensor with isopropyl alcohol. First coat of plastic primer, couple of top colour coats and followed by a couple of clear lacquer flash coats. Read you can cure paint by popping in oven for a few minutes (without the rubber ‘o’ ring, but think I’d miss that part out, and just don’t jet-wash directly for a few weeks.