Scientists trying to take advantage of the unusual properties of the quantum realm say they have successfully simulated a method of backward time travel that allowed them to change an event after the fact one out of four times. The Cambridge University team is quick to caution that they have not built a time machine, per se, but also note how their process doesn’t violate physics while changing past events after they have happened.
The problem I’m going to assume applies here is the same as why we can’t train self-driving cars with a simulation. It’s a paradox; if the simulation was robust enough to train cars for the real world, then creation of the simulation itself WOULD be the solution since it already knows all the rules and correct reactions.
In other words, I’m sure they got their simulation to work, within the confines of a limited, non-paradoxical, error-prone programming.