It’s rather simple to do the so called ’gain of function’, you let the virus have it’s run with bat cells and add lots of human cells in petri with them. Because there is no immune system, the virus have not much to stop it. Slowly it adapt to human cells, you can change the type of cells so it can adapt to other receptors and so on. Those articles where published before the whole crisis erupted.
One of the keys there is that's not uniquely Chinese as a problem. Those researchers were talking about American labs.