After finding the Higgs boson, hints at new physics at the LHC are scarce. An exception are the $B$-anomalies found by LHCb in $R_K$ and $R_{K^{\ast}}$ measurements, the latter two combining to a 4 sigma deviation from the SM. A possible explanation of this excess might be a new heavy neutral gauge boson $Z'$ with flavour-conserving couplings to second and third generation leptons, as well as third generation quarks, in addition to a flavour-violating b-s coupling. This talk covers search strategies and challenges for such a hypothetical particle in the dimuon channel at CMS.