It starts with a “DPF delete” kit, which allows the user to remove the diesel particulate filter in the exhaust system. These have been commercially available for some time, championed largely by truck owners who don’t like the exhaust restriction, power loss, and maintenance that results from having that filter in place. Modifying emissions components like this is illegal, and the EPA has been working hard to get these things off the market.
The DPF delete kit by itself is not enough to roll coal. AIUI, the “lie” told to the ECU that makes the magic happen has to do with manifold pressure: if you convince the ECU that the engine is at high turbo boost, then it’ll inject all the fuel you ask it to when you step on the accelerator. If the boost isn’t actually that high, then you’ll end up with a rich mixture and make black smoke. I expect you’d need to spoof the manifold pressure sensor, and also do something to limit the boost - either open the wastegate, or disable the variable geometry feature (if it’s present on the turbocharger in question).