There should be an "x" between Cash and Influence on the parchment holder. Press that and skill classes will reset back to 0. :)
Right, I did find that. I mean just an option to deselect each individual choice rather than resetting the entire thing which you can't even do if you have made any other selections on the attribute or trait menu. Those can be changed after selection, I just find it odd and tbh annoying that you can't unselect a skill class.