If you're a gambler, then control and manage how you're gambling before it get worse to the extreme stage, also, if you're privileged to see someone gambling in the wrong direction, take it a responsibility to call them into order, some things were better done or dealt with in the early stage before they got worsened, having desires for gambling is not getting yourself harmed by gambling because if ignorance or lack of self control while gambling, the gambling platforms will not control you, it's your own responsibility to do so for yourself.
It is very rare that people listen to others when it comes to this as they will feel judged, and they will think that you are overstepping their boundaries by doing something like this, so even if you were correct on your observations about their gambling habits, you can bet they will continue to gamble as usual, and even if at some point they realize they had a problem you can be sure they will not remember that you tried to help them before things got out of control.