So the code in question is the MainActivity.java file. By default, the line code must’ve looked like this:

public class MainActivity extends ReactActivity {

The React Native upgrade helper says I need to change it to this:

class MainActivity : ReactActivity() {

The problem is that my line actually looks like this:

public class MainActivity extends ReactActivity implements APIGuard.InitializationCallback {

As you can see there’s an additional implementation, so I am not sure how to handle that with the new syntax.