Heat a large skillet over medium heat. Add beef; cook until completely browned, about 5 minutes. Season with salt and black pepper; transfer to a slow cooker, retaining some drippings in the skillet.

Heat drippings in skillet; add onion and garlic. Sauté until softened, about 5 minutes; add to slow cooker.

Stir potatoes, diced tomatoes, sofrito, and olives into beef mixture.

Cook on Low until beef and potatoes fork-tender, 4 to 5 hours.