How to assign values to below Object

Hi

  I have below object . How i can assign values and then serialize using restsharp

    public class BuyerDtls
    {
        public string Gstin { get; set; }
        public string LglNm { get; set; }
        public string Pos { get; set; }
        public string Addr1 { get; set; }
        public string Loc { get; set; }
        public int Pin { get; set; }
        public string Stcd { get; set; }
    }

    public class DispDtls
    {
        public string Nm { get; set; }
        public string Addr1 { get; set; }
        public string Loc { get; set; }
        public int Pin { get; set; }
        public string Stcd { get; set; }
    }

    public class DocDtls
    {
        public string Typ { get; set; }
        public string No { get; set; }
        public string Dt { get; set; }
    }

    public class ItemList
    {
        public int ItemNo { get; set; }
        public string SlNo { get; set; }
        public string IsServc { get; set; }
        public string PrdDesc { get; set; }
        public string HsnCd { get; set; }
        public int Qty { get; set; }
        public int FreeQty { get; set; }
        public string Unit { get; set; }
        public int UnitPrice { get; set; }
        public int TotAmt { get; set; }
        public int Discount { get; set; }
        public int PreTaxVal { get; set; }
        public int AssAmt { get; set; }
        public int GstRt { get; set; }
        public int IgstAmt { get; set; }
        public int CgstAmt { get; set; }
        public int SgstAmt { get; set; }
        public int CesRt { get; set; }
        public int CesAmt { get; set; }
        public int CesNonAdvlAmt { get; set; }
        public int StateCesRt { get; set; }
        public int StateCesAmt { get; set; }
        public int StateCesNonAdvlAmt { get; set; }
        public int OthChrg { get; set; }
        public int TotItemVal { get; set; }
    }

    public class Root
    {
        public string Version { get; set; }
        public TranDtls TranDtls { get; set; }
        public DocDtls DocDtls { get; set; }
        public SellerDtls SellerDtls { get; set; }
        public BuyerDtls BuyerDtls { get; set; }
        public DispDtls DispDtls { get; set; }
        public ShipDtls ShipDtls { get; set; }
        public List<ItemList> ItemList { get; set; }
        public ValDtls ValDtls { get; set; }
    }

    public class SellerDtls
    {
        public string Gstin { get; set; }
        public string LglNm { get; set; }
        public string Addr1 { get; set; }
        public string Loc { get; set; }
        public int Pin { get; set; }
        public string Stcd { get; set; }
    }

    public class ShipDtls
    {
        public string Gstin { get; set; }
        public string LglNm { get; set; }
        public string Addr1 { get; set; }
        public string Loc { get; set; }
        public int Pin { get; set; }
        public string Stcd { get; set; }
    }

    public class TranDtls
    {
        public string TaxSch { get; set; }
        public string SupTyp { get; set; }
        public string RegRev { get; set; }
        public string IgstOnIntra { get; set; }
    }

    public class ValDtls
    {
        public int AssVal { get; set; }
        public int CgstVal { get; set; }
        public int SgstVal { get; set; }
        public int IgstVal { get; set; }
        public int CesVal { get; set; }
        public int StCesVal { get; set; }
        public int Discount { get; set; }
        public int OthChrg { get; set; }
        public int RndOffAmt { get; set; }
        public int TotInvVal { get; set; }
    }

Thanks