ReactOnCreate.java

import com.millennialmedia.MMException;
import com.millennialmedia.MMSDK;
import com.millennialmedia.AppInfo;

...

private static final String SITE_ID = "[YOUR_SITE_ID]";

...

@Override
public void onCreate() {
  super.onCreate();
  SoLoader.init(this, /* native exopackage */ false);

  //Initialize the Millennial SDK
  try{
      MMSDK.initialize(this);

     //Set Site ID
     AppInfo appInfo = new AppInfo();
     appInfo.setSiteId(SITE_ID);
     MMSDK.setAppInfo(appInfo);

  } catch (MMException e){
      Log.e(TAG, "SDK didn't initialize", e);
  }
}