This is a difficult question. I think that the presidents of these countries need to be aware of the damage their nations are causing. Once, they have been taught about pollution they need to see, first hand, what pollution is doing. They need to see the statistics and learn about how plastic is harming humans as well as marine life. These countries need people to teach these things and inform all generations of how they can protect what belongs on this planet. We need to share the planet with creatures that were here thousands of years before us. Pollution isn't going to end overnight but, overnight we can make a start. People with power must influence others to reduce their plastic use and recycle.
These leaders are also very driven by the economic outcome of their countries. If they understand that their countries can benefit from creating 'green' goods, then perhaps they would be more open to climate friendly ideas. The USA have an election coming up and I hope to see a change in environmental policies.