To make money from bitcoin crash is join some bounty campaign to earn even tje bitcoin is crash or the price in the market is dump. You can also join some airdrops to earn but when earning in airdrops you need to dOK first the task and refer many so that you will earn big. It is worth if you can refer many so your reward is big and you will not earn small.
How to make money from decreasing bitcoin prices, which is holding bitcoin to wait for prices to rise and sell. If prices continue to fall, bitcoin sells then buys again at a lower price, the difference is profit. Indeed, it takes courage and luck.