I found all I can find ,but I still no answer.pls help me.

        void SpawnObject(string obj, Vector3 das, bool dyn=false)
        {
			NetworkInstantiateConfig prefabES = null;
			foreach (NetworkInstantiateConfig prefabs in Resources.FindObjectsOfTypeAll<NetworkInstantiateConfig>())
			{
                if (prefabs.name.ToString() == obj)
                    prefabES = prefabs;
			}
            GameObject Obj = Singleton<HNetworkManager>.Instance.NetInstantiate(prefabES, das, Quaternion.identity, GameManager.GetSceneTime());
            if (dyn==true)
            {
                Rigidbody rigit = Obj.GetComponent<Rigidbody>();
                rigit.ResetCenterOfMass();
                rigit.constraints = RigidbodyConstraints.FreezeAll;
                timer.Once(4.5f, () =>
                {
                    rigit.ResetCenterOfMass();
                    rigit.constraints = RigidbodyConstraints.None;
                });
            }
            if(Obj == null)
            {
                Server.Broadcast("error");
                return;
            }
        }

Mozzy string  = MozzyTownChassisSpawner

It has not been verified whether it works