We could just sell them opium. It worked for the Brits for a good long while.
it's important for everyone to realise that there are no good guys or bad guys in the world, there are just people (or nation-states, in this case) looking out for their own self-interest, which is what one would expect. Did/is the CIA involved in the HK uprisings? Idk, maybe. It's not like it's unheard of (re: Cold War South America, Iran, etc). Regime change is one the many things they do. Is it also, equally likely, that after nearly a century of being not Chinese, and not identifying themselves as Chinese, but as Hong Kongers, that the Hong Kong people themselves are not in favour of being under Chinese rule, and all the things that come with it? Yeah of course.
What to *do* about China? Probably nothing. China is the most powerful country in the world. Sure, the US has a better military, but China controls the purse. It also has UNSC seat, which it won't ever lose because Russia would veto it with it's veto power. I don't want to sound like a China apologist, but China does most of the shitty things it does to it's own population (ignoring Tibet). The US does awful things to populations outside it's borders (minus the shitty things cops do and the border detentions, although they aren't US citizens, but still abhorrent). Should the US be the only hegemonic power in the world? Probably not, because that's too much power. America's influence is already on the decline, globally, because we have a manchild president who doesn't know how the world works, and as such, many countries turn to China or Russia for aid because it gets those developing nations the help they need and gives both Russia and China influence. China basically owns Africa at the moment. It is doing exactly what the US did in the Cold War with the IMF. Saddling them with loans for infrastructure, but instead of insisting on the installation of neoliberal or capitalist values, it is demanding resources and access to shipping ports to develop it's new Silk Road initiative. America has largely missed the boat on Africa because while we were busy in the geopolitical clusterfuck that is the 'War on Terror', China was busy making endroads with countries from Mauritania to Mozambique.
China, as all oppressive regimes have in the passed, will eventually face the reality that change is inevitable. Once people's standards of living start to slip or stagnate, there will be calls for change, and even if there is violence, eventually concessions will have to be made. It's happened 1000 times before and will happen 1000 times again. For now, though, most people are happy to go about their lives, as they are in the west because the standard of living is comfortable enough and if they don't make waves, they can hold onto that. We have the same problem in America of people being pacified by bread and circuses (although the two scenarios vary massively).
Fun fact, during Thatcher's term, she did not want to give HK to China, but she didn't have much of a choice. China could have simply invaded and took it for itself if it wanted to, and she realised the reality of the situation and capitulated. The same is true today, although there is more international pressure, there really isn't anything anyone could do stop a full scale invasion from happening and I don't think any western country is keen to get into a war with China for anything, even HK.