You can hide Ads by selecting the down arrow menu or the 'x' in the top right-hand corner of the sponsored post. That means that once you’ve blocked an Ad, you won’t see it again. There is not yet a single button to block all adverts categorised as ‘gambling’ so you may need to do this to separate gambling companies or separate advertising campaigns by the same company.
In addition, you can adjust your ads preferences to see Ads that are more relevant to you. To find more information regarding 'can I block Ads' on Facebook and 'how can I adjust my Ad preferences', please view this article from their Help Center. Your settings can be found here.
Please note, this advice is not comprehensive as social media sites may change their operating policies from time to time. There is also no guarantee that information and settings will be carried over between devices (e.g. shared devices between family members). If you are worried about problem gambling, you may find it appropriate to exclude yourself from gambling directly. You can find out more about account closures, Self-Exclusion and the organisations in place to help you here.