Heat a large skillet over medium heat. Cook beef in hot skillet until completely browned, about 5 minutes; season with salt and pepper. Transfer beef to a slow cooker, retaining some of the beef drippings in the skillet.
Return skillet to heat and heat the retained drippings. Saute onion and garlic in hot drippings until softened, about 5 minutes; add to beef in slow cooker.
Stir potatoes, diced tomatoes, sofrito, and olives into the beef mixture.
Cook on Low until beef and potatoes are fork-tender, 4 to 5 hours.