Add additional quality of service channel modes to NetworkManager

Unity Engine
1

I need to add a few additional quality of service channel modes to NetworkManager and I’m attempting to do it in this way:

 NetworkManager netMan;
  
    void Start () {
    ConnectionConfig cc = new ConnectionConfig();
  
    reliableChannel = cc.AddChannel(QosType.Reliable);
    reliableSeqChannel = cc.AddChannel(QosType.ReliableSequenced);
    reliableFragChannel = cc.AddChannel(QosType.ReliableFragmented);
    unreliableChannel = cc.AddChannel(QosType.Unreliable);
    unreliableSeqChannel = cc.AddChannel(QosType.UnreliableSequenced);
    cc.PacketSize = 1440;
  
    netMan.connectionConfig = cc;
    }

But I’m getting the error : Property or indexer 'NetworkManager.connectionConfig' cannot be assigned to -- it is readonly

If the property is read-only then what is the proper way to create additional channels to NetworkManager?

…full function below

using System.Collections;
    using System.Collections.Generic;
    using UnityEngine;
    using UnityEngine.Networking;
  
    public class Server : MonoBehaviour {
  
        public Texture2D textureToSend;
        string messageToSend = "Test Message";
  
        NetworkManager netMan;
  
        private int reliableChannel;
        private int reliableSeqChannel;
        private int reliableFragChannel;
        private int unreliableChannel;
        private int unreliableSeqChannel;
  
        // Use this for initialization
        void Start () {
  
            ConnectionConfig cc = new ConnectionConfig();
  
            reliableChannel = cc.AddChannel(QosType.Reliable);
            reliableSeqChannel = cc.AddChannel(QosType.ReliableSequenced);
            reliableFragChannel = cc.AddChannel(QosType.ReliableFragmented);
            unreliableChannel = cc.AddChannel(QosType.Unreliable);
            unreliableSeqChannel = cc.AddChannel(QosType.UnreliableSequenced);
            cc.PacketSize = 1440;
  
            netMan.connectionConfig = cc;
  
            NetworkManager.singleton.StartHost();
            Debug.Log("Server Started.");
        }
  
        public void SendOnButtonPress()
        {
            SendTexture(textureToSend, messageToSend);
        }
  
        //Call to send the Texture and a simple string message
        public void SendTexture(Texture2D texture, string message)
        {
            TextureMessage msg = new TextureMessage();
          
            //Convert Texture2D to byte array
  
            msg.textureBytes = texture.GetRawTextureData();
            msg.message = message;
  
            NetworkServer.SendToAll(MyMsgType.texture, msg);
        }
    }
2

AFAIK you can do this via Inspector without any code. Tick Advanced Configuration checkbox.