We investigate B?L gauge extension of Standard Model where a B?L charged scalar is a viable dark matter candidate and its dominant annihilation process is through the B-L breaking scalar to a right-handed neutrino pair. We exploit the effect of decay and inverse decay of the right-handed neutrino in thermal relic abundance of the DM, which enlarges the parameter space satisfying the DM relic density significantly. For a DM mass less than O(TeV ), the direct detection experiments impose a competitive bound on the B?L gauge boson mass with the collider experiments. Based on the predicted displaced decays of the right-handed neutrino, the search limits on the B-L gauge boson have been obtained at present and higher luminosity LHC.