Bring a large saucepan of salted water to a boil. Add the collard greens in batches and cook until tender, about 10 minutes. Using a slotted spoon, transfer the greens to a colander and rinse under cool water. Squeeze the leaves to remove any excess water.
Heat the oil in a large saucepan over medium heat. Add the garlic and cook for 1 minute. Add the greens, salt, and pepper. Cook, stirring frequently, until wilted and tender, 3 to 4 minutes.
In Advance: Rinse the greens, pat them dry, and slice. Wrap in a clean kitchen towel or place in a resealable bag and refrigerate for up to 24 hours.