The A Friend in Deed side quest in Hogwarts Legacy becomes available during the main quest to Prepare for Your Search for the Final Keeper main chapter after completing a few of the main quests. It can be obtained from Sirona Ryan at the Three Broomsticks in Hogsmeade. Speak with her there and she’ll ask you to check up on her old friend Mrs. Sprottle along with grabbing a box of her stuff while you’re there.
Travel to Upper Hogsfield to find Mrs. Sprottle tending to her vegetable garden. Speak with her and she will ask you to assist with collecting Horklumps for her. She will also mention that her husband dropped the box of letters in a cavern southwest of the hamlet in the hills. Set out for this cavern (Horklump Hollow) on your broomstick then head inside.
Follow the path by burning the vines along the way with fire spells and breaking objects with Depulso to progress. Make sure to collect the Horklumps you come across along the way. Eventually, you’ll end up in a giant room with a troll. You can either defeat it or sneak past it. Near the exit of the cavern, you’ll find the crate and 5 letters scattered on the ground nearby. Collect them then return to Mrs. Sprottle to deliver the plants. After that, bring the letters to Sirona to complete the quest. You’ll receive a Keg Shelf configuration.