Just let them continue gambling until they stop on their own without any instruction or advice, especially if they have a family. It will be a devastating blow to see their family suffer as a result of their poor decisions, assuming they can turn things around on their own.

Reminding someone like an addict is very difficult. When their balance is low or empty, they might stop, but when they have more funds, they will inevitably continue because, in their minds, that's all that comes to mind, just like when we open social media and watch a football game, football is always the first thing on the page.