Lattice sites and annealing behavior of implanted ${}^{12}\mathrm{N}$ in semi-insulating ZnSe are investigated by use of \ensuremath{\beta} radiation detected nuclear magnetic resonance (\ensuremath{\beta}-NMR). For room-temperature implantation only a small part of the N impurities is found at sites with full ${T}_{d}$ symmetry; this fraction is attributed to substitutional ${\mathrm{N}}_{\mathrm{Se}}.$ Above 500 K the population of this site increases and saturates at a 10 times higher value for $Tg~950\mathrm{K}.$ This increase is assigned to the change of initially interstitial N $({\mathrm{N}}_{i}),$ isolated or part of a complex, to unperturbed ${\mathrm{N}}_{\mathrm{Se}}.$ An activation barrier ${E}_{a}=0.47(5)\mathrm{eV}$ is determined for this process representing an upper limit for the ${\mathrm{N}}_{i}$ migration energy. We do not observe configurations where ${\mathrm{N}}_{\mathrm{Se}}$ is bound to a diamagnetic partner, like the ${(V}_{\mathrm{Se}}{\ensuremath{-}\mathrm{Z}\mathrm{n}\ensuremath{-}\mathrm{N}}_{\mathrm{Se}}{)}^{+}$ complex.