Basically, by shorting it. But there are only few shitcoins that are been listed on futures market so it is really hard to pick altcoins that are been collapsing. Before I catch up the huge dump in FTX because of its scandal where I shorted it with low margin and I earn bucks from it. Try to research coins that are been listed on futures market with bad team and with bad services because usually those coins are good for shorting.

But don't always do shorting because your psychology can be destroyed it is better also if you will do long market but make sure that you have a good trading plan and strategies that you could use to make profit in the market. Finding the right altcoin for long market is also hard to find so better you have knowledge and set of unique skills that you can use in order to pick the right coin that you will short or long.