After removing a person from the initial environment he knows gambling then his family provides support by making someone do other activities that he likes.
Some people can also easily stop their addiction by themselves, but that's only if they are made to realise how bad their lives have become because of their addiction habit. Some people don't even realise that their gambling addiction is so bad. To me, it seems some people lose their sense of reasoning properly, and they don't even care how much they lose; they don't care about adding value to their lives; they just totally lost everything. So first of all, they just need to be made to realise themselves, and they can gradually stop. Some people make it more difficult for themselves in the sense that they can't even listen to anyone cautioning them, and as such, they can't even get help from their loved ones.