@rasputin177: You should check the item description (On ps4 it requires you to press Square while the pyro flame is highlighted) I don't know the Keybinding and I'd assume the Xbone would be X.
In the description it usually tells you "Can be used in either hand" or not. If it doesn't, you probably can't. ( though some weapons, when equipped in the right hand, require you to press Triangle/Y/keybinding(i still don't know) to two hand it and then you can use the weapon art.
Hope this helps.