So how to unlock Inventor's transmuitation skill?

I feel like I’ve finished half of FG already… Which quest unlocks it?

Edit: This is insane! I’ve explored over 60% of the FG map aтв I still can’t transmute goddamn sets. This feature is poorly designed…

Edit 2: Indeed there is a small quest you have to finish, but first you have to uncover ~50% of the map… My chars are overloaded with duplicates, I just wanted to transmute everything right from the start.

Well, you can just go in with a 100th level character on Normal and rush through the game to unlock it. Then have that character do the transmuting.

LOL patience is not your strong side I see