To the best of my understanding CoMP is not currently supported by NetSim. Their website also doesn't mention CoMP
However, it might be possible to modify the C codes to get this functionality. You need a way of differentiating between UEs that will be handled by a single gNB and UEs that will be handled by multiple gNBs (CoMP) And then you would need the algorithm for coordinated scheduling (to determine which set of gNBs should serve multi-gNB UEs.