How-to-cut-position-after-a-X-gain-loss

Maybe this is the example that you were looking for. You can define the symbol, shares, price, and date you entered a position and then trade the position with a script. Here, we enter 100 shares of "U" at 100.20 using OrderType.FixedPrice and sell half the shares after a 50% loss, on a closing basis.

CODE:
using WealthLab.Backtest;
using System;
using WealthLab.Core;
using WealthLab.Indicators;
using System.Collections.Generic;

namespace WealthScript123
{
    public class LoadAndSellPositionDemo : UserStrategyBase
    {
        //create indicators and other objects here, this is executed prior to the main trading loop
        public override void Initialize(BarHistory bars)
        {
         StartIndex = 1;
         PlotStopsAndLimits(3); 
        }

        //execute the strategy rules here, this is executed once for each bar in the backtest history
        public override void Execute(BarHistory bars, int idx)
        {
         if (bars.Symbol != _symbol)
            return; 
         
            if (!HasOpenPosition(bars, PositionType.Long))
            {
            // enter the trade hypothetically
            if (bars.DateTimes[idx].Date == _dte)
            {
               Transaction tn = PlaceTrade(bars, TransactionType.Buy, OrderType.FixedPrice, _price);
               tn.Quantity = _shares; 
               _stopped = false; 
            }            
            }
            else
            {
            // sell half on a 50% stop
            Position p = LastPosition;
            if (!_stopped && p.ProfitPctAsOf(idx) <= -50)
            {
               Transaction tn = PlaceTrade(bars, TransactionType.Sell, OrderType.Market, 0, "Stop 50%");
               tn.Quantity = p.Quantity / 2;
               _stopped = true; 
            }
               else if (p.ProfitPctAsOf(idx) > 50)
            {
               ClosePosition(p, OrderType.Market, 0, "Profit Tgt");
            }   
            }
        }

      // example trade data
      string _symbol = "U";
      DateTime _dte = new DateTime(2022, 4, 5);
      double _price = 105.20;
      int _shares = 100;
      bool _stopped = false; 
    }
}

Also see Trade History Strategies that let you analyze a trade history by reason a set of trades from a file.