Stop, simply as that. Just like any addiction, if you have the will power then you can overcome your addiction. Worst case is that you seek medical help, but there's no need for it. Just quit !!!
There is more to it than just the will to stop. I'm sure a lot of these people badly want to stop, but there is nothing in their life that they can focus on than in this case trading/investing in crypto currencies.
People that manage to stop do it because they can focus on other things, but when you don't have anything to live for (I know it sounds serious), they will keep doing whatever it is just to stay busy.
An addiction always has an underlying cause that people from outside the circle of the addicted person tend to ignore, hence keep saying why don't you just stop, it's so easy when you really want it, and so forth.