Script preview gives you a glimpse of how your strategy would execute during a preview. It runs your script on the last 5000 candles. You can open up the settings of the preview by clicking the little cog in the bottom right under the chart.
Once you click on it, it opens up a window to backtest, run paper trade or live trade and at the bottom, we have an update preview button.
Just click on it, and it gives a preview of the last 5000 candles. You can also refresh your script performance preview by clicking on a small icon just above the terminal.