...
include ':react-native-des'
project(':react-native-des').projectDir = new File(rootProject.projectDir, '../node_modules/react-native-des/android/RCTDes')

...
dependencies {
    ...
    compile project(':react-native-des')
}

import com.remobile.des.*;  // <--- import 
 
public class MainActivity extends Activity implements DefaultHardwareBackBtnHandler {
  ......
 
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mReactRootView = new ReactRootView(this);
 
    mReactInstanceManager = ReactInstanceManager.builder()
      .setApplication(getApplication())
      .setBundleAssetName("index.android.bundle")
      .setJSMainModuleName("index.android")
      .addPackage(new MainReactPackage())
      .addPackage(new RCTDesPackage())              // <------ add here 
      .setUseDeveloperSupport(BuildConfig.DEBUG)
      .setInitialLifecycleState(LifecycleState.RESUMED)
      .build();
 
    mReactRootView.startReactApplication(mReactInstanceManager, "ExampleRN", null);
 
    setContentView(mReactRootView);
  }
 
  ......
 
}