The first step is to figure out exactly where the discrimination is occurring. Simply observing differences in outcomes doesn't tell us where the discrimination is happening---in some cases it's not even happening at the institutions we are looking at, but in society as a whole. More often, there are several layers of discrimination people are subjected to from multiple sources.
For example, only a small portion of the wage gap between men and women is explained by active discrimination in hiring practices; the majority is due to differences in societal gender roles that drive men and women into different professions and result in higher pay in male-dominated professions. Active discrimination creates a gap of about 4%, but gender roles and other factors make the total gap closer to 30%.
With this in mind, we would first need to make sure that our police officers actually are discriminating against racial minorities, and not simply responding to inequities created by society at large. Many policies that disproportionately affect racial minorities are actually race-blind policies, but have disproportionate impact due to the overall inequality of society. Some such policies can be reformed, but others are unavoidable; a certain racial disparity in arrests and imprisonments is going to exist as long as there is the same disparity in rates of poverty and crime, and it would be perverse for it not to. Ultimately we need to fight the disparity in poverty and crime.
But suppose we find evidence that the police are indeed actively discriminating; the next step is to figure out how they are discriminating---who is doing it to whom and why.
Some discrimination is intentional, committed by avowed racists; on the principle that "one bad apple spoils the bunch", the police have reason to find any such individuals and fire them unless they reform on a reasonable timetable. But a good deal of discrimination is not of this form, but instead involves much subtler subconscious biases that are harbored by almost everyone, even those of us who morally abhor racism.
These subconscious biases can't really be countered by conscious attempts at improving behavior. Instead what we must do is either make decisions race-blind so that subconscious biases can't even take hold (for example, when hiring new officers, remove all names and photos from resumes to avoid revealing race and gender), or else fight subconscious with subconscious, using psychological techniques to prime people with ideas that run counter to their subconscious stereotypes. If they view Black people as criminal, for example, show them images of Black people being upstanding, law-abiding citizens (and perhaps of non-Black people as criminals). If they view Black people as unintelligent, show them examples of highly intelligent Black people (Neil deGrasse Tyson, for instance). This kind of exposure is the best method we have for countering subconscious stereotypes, and probably part of the reason why rising exposure of a given group in the media is linked to better acceptance for that group by the public at large.
This could be done as part of a more comprehensive mandatory diversity and sensitivity training, where officers are taught to avoid using offensive language such as racial slurs and sexist jokes, and trained in techniques for interacting with people of different languages and cultures (particularly important for White officers in areas with large Hispanic populations). This training must absolutely be mandatory, because those who need it most are those who are most likely to try to avoid it. Nor may any excuses be accepted from those who try to defend the use of bigoted language as "just a joke" or "part of camaraderie"; this subtle bigotry reinforces the subconscious stereotypes that can have serious real effects on behavior.
These policies, combined with more general reforms such as community policing, decarceration, and demilitarization, would surely not eliminate racism in a community, but could substantially reduce the harm it causes.