How to access the private field in child class ?

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C#

class Customer
    {
        protected int _cid, _bal, _status;
        private string _cname;
 

        public Customer(int _cid, int _bal, int _status, string _cname)
        {
            this._cid = _cid;
            this._bal = _bal;
            this._cname = _cname;
            this._status = _status;
        }
 
        public int Cid
        { //read only property
            get
            {
                return _cid;
            }
 
        }
        public virtual string Cname
        {
            get
            {
                return _cname;
            }
            set
            {
                if (_status != 0 & _bal >= 500)
                {
                    _cname = value;
                }
            }
        }
        public int Bal
        {
            get
            {
                return _bal;
            }
            set
            {
                if (_status != 0 & value >= 500)
                {
                    _bal = value;
                }
            }
        }
        public int Status
        {
            get
            {
                return _status;
            }
            set
            {
 
                _status = value;
            }
        }
        public virtual void display()
        {
            // Console.WriteLine("id={0} and name={1} and balance={2} and status={3}",Cid,Cname,Bal,Status);
            Console.WriteLine("id={0} and name={1} and balance={2} and status={3}", _cid, _cname, _bal, _status);
        }
    }
 class Specialcustomer : Customer
    {
        public Specialcustomer(int _cid, int _bal, int _status, string _cname)
            : base(_cid, _bal, _status, _cname)
        { 
          }
        public override string Cname
        {
            get
            {
                return _cname;
 
            }
 
            set
            {
                if (value == "Special")
                {
                    _cname = value;
                }
            }
        }
 
        public override void display()
        {
            
Console.WriteLine("id={0} and name={1} and balance={2} and status={3}", Cid, Cname, Bal, Status);
        }
    }
static void Main(string[] args)
        {
            Customer C1 = new Specialcustomer(10, 400, 1, "BOND");
            C1.display();
            C1.Cname = "Special";
            C1.display();
            Console.ReadKey();
        }

What I have tried:

in this example
when i was using

_cname

as protected field it was working fine but when i changed it to private it is giving me error.so how can i access the

_cname

in child class if i changed the field to pvt. without using Reflection.

and if i changed _cname to base.Cname in Special Customer class Overriding is not happening as it going to base property