I wasn't there wen they learned that- [Mako and Korra were there... but she should clarify] I was out stopping the Equalist's airforce with Bolin and General Iroh. [just to make sure she know that she knows the story of Amon's power secondhand. But she witnessed it firsthand]

But... if you mean how we learned to reverse it, that was in the south pole. With you, actually.