  We used \emph{in-situ} potassium (K) evaporation to dope the surface of the
iron-based superconductor FeTe$_{0.55}$Se$_{0.45}$. The systematic study of the
bands near the Fermi level confirms that electrons are doped into the system,
allowing us to tune the Fermi level of this material and to access otherwise
unoccupied electronic states. In particular, we observe an electron band
located above the Fermi level before doping that shares similarities with a
small three-dimensional pocket observed in the cousin, heavily-electron-doped
KFe$_{2-x}$Se$_2$ compound.
