You'll have to do it on the next difficulty. There's no way to do the quest again on the same difficulty. To respec your character, all you need to do is visit the main NPC at the first area, talking with them, and you will have the option to respec. How to reset skills and stats in Diablo 2 Resurrected The first such way is to complete the Den of Evil quest.
From PatchDiablo 2 players can now respec there are two ways to perform a respecialization.
