There are professional ways to repair leather, but if it was myself I would micro-dab some dark colour into the small area. Use a sharp pointy toothpick like object, dab it into some coloured product and then dab it into the damaged area carefully, smooth off the excess. Maybe some shoe-polish, or Permatex makes a vinly repair kit with some coloured product in it. I'd suggest a sharpie marker but you need to be careful with it going over the lines too much, hence why I like micro-dabbing for small repairs.