The lows of the candle should be the low of the downtrend. This is usually preceded by a minimum of four consecutive lower low candles prior to the bullish engulfing candle, which should close near the candle highs. When the next candle closes above the bullish engulfing candle, it forms a market structure low trigger, which is the high of the proceeding candlestick. When that high is broken, then an official trend reversal forms.