If we suspect that the US stock market to burst soon, how should we pivot our portfolio such that when the burst comes, we can gain from it?

Just DCA diligently. DCA will not fail you if you consistently carry it out over the long run. The market never fails to recover!

I do agree with most of the posters who mention you should consider just dca instead of timing the market. However, if you do wish to gain through swing trades, you can consider holding a larger proportion of your portfolio in cash right now by selling off the stocks you currently own, waiting till the burst before buying back the stocks at a cheaper price. (not neccessary the bottom as it is hard to catch the bottom)