The Beeting a Curse side quest in Hogwarts Legacy becomes available during the Stop Ranrok and Rookwood main objective. Travel to the Greenhouses Floo Flame in the Library Annex during the day and speak with Samantha Dale. She tells you her brother has been cursed and asks you to help out.
Exit Hogwarts and head for the Dale Family Tomb, east of Brocburrow. Head inside the work your way to the doorway covered in Devil’s Snare. Use Lumos to head through the drop down into the area below. Here you’ll have to fight a troll guarding the tomb. From the troll room, if you head southwest, there will be a path with a wall at the end you can break. This will lead you to an area with a collection chest. Heading southeast will take you to the sarcophagus where you can return the crest to Marmaduke. You may want to do that before getting the collection chest to prevent you from having to backtrack.
After returning the crest, head back to Samantah and speak with her to complete the quest. You’ll receive a totem conjuration as a reward.