The Follow the Butterflies side quest in Hogwarts Legacy becomes available during the Complete the First Keeper Trial main quest. Travel to Hogsmeade then make your way to the Three Broomsticks. Speak with Clementine Willardsey near the broom rack. She’ll ask you to follow some butterflies into the Forbidden Forest to see where they go. Agree to help her then travel to the Forbidden Forest Floo Flame. Head under the archway and across the bridge following the path into the forest. After progressing a short way, you’ll come across a group of butterflies. Follow them through the forest and eventually, they’ll make a chest appear.
Open it to receive a Small Potion Station conjuration. Return to Clementine to report your findings completing the quest. You’ll also receive a Flower Box conjuration.