We see that the symmetry axes for the Fe-I atoms are: the axis perpendicular to the plane determined by the Fe-IIa atoms, the axis going from one Fe atom the its counterpart at the other side, right trough N, the axis that goes through N and two collinear Fe-IIa atoms.
For the FeIIa atoms the symmetry axes are once again the axis perpendicular to the plane they make, the axis through to collinear atoms of FeIIa and N of course. Note that in this configuration, the diagonal axis are not symmetry axes.