A stock has bottomed out when it stops making lower lows, prints a higher low, holds key support on rising volume, and shows momentum divergence with bullish reversal candles confirming the shift. You need a "cluster of indicators" to buy and sell, meaning more than one indicator confirming the move.
Look for a bullish candlestick at the close, such as a hammer with a long wick, or better yet, a candle that closes at the day's highs after bouncing at least 5% from its lows.
Momentum divergence, where price is still falling but the rate of decline slows relative to recent history, gives clues about trend strength.
Wait for confirmation rather than guessing the absolute low.