MainApplication.java

// alter your android/app/src/main/java/com/cppreactnative/MainApplication.java

import com.cppreactnative.helloworld.HelloWorldPackage; // Add this import statement

//...

@Override
protected List<ReactPackage> getPackages() {
  return Arrays.<ReactPackage>asList(
      new MainReactPackage(),
      new HelloWorldPackage() // add this line to the list of packages.
  );
}