Making money from the fall
There are two ways to cash in. If you believe that Bitcoin is about to collapse. Before the two ways if you're convinced that Bitcoin will crash or you're worried about it then you should sell them. Even if you are later proved wrong you will at least have a profit(a small profit is always better than a loss)
Method one
1-First one is very simple as you can bet on the crash, This can be done with a contract for difference or spread bet at a range of exchanges.
Method two
2-could try short-selling
Taking a “short” position involves borrowing some Bitcoins, selling them on at prices now, then buying new bitcoin at the decreased price to replace the older ones you've sold when the time comes to return bitcoin to original owner.
If the price fall you could make a good profit but if the price has surges you'll have to pay both for borrow the coins and the rise in price from when you borrowed them.