You may set an alert with the condition when the stock price crossing down the Stop Price.
stock price: $150
current ATR: $3
stop price = $150 - $3 * 2 = $144
add-position price = $150 + $3 * 2 / 2 = $153
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.