code: @POST
      @Path("/bulk")
      @Consumes(Servlets.JSON_MEDIA_TYPE)
      @Produces(Servlets.JSON_MEDIA_TYPE)
      public EntityMutationResponse createOrUpdate(AtlasEntitiesWithExtInfo entities) throws AtlasBaseException {
          AtlasPerfTracer perf = null;
  
          try {
              if (AtlasPerfTracer.isPerfTraceEnabled(PERF_LOG)) {
                  perf = AtlasPerfTracer.getPerfTracer(PERF_LOG, "EntityREST.createOrUpdate(entityCount=" +
                                                                 (CollectionUtils.isEmpty(entities.getEntities()) ? 0 : entities.getEntities().size()) + ")");
              }
  
              EntityStream entityStream = new AtlasEntityStream(entities);
  
              return entitiesStore.createOrUpdate(entityStream, false);
          } finally {
              AtlasPerfTracer.log(perf);
          }
      }
docs: Bulk API to create new entities or update existing entities in Atlas.
  Existing entity is matched using its unique guid if supplied or by its unique attributes eg: qualifiedName