I didn't have a chance to make mobile package from VNM, but it uses Cordova to build the game on both iOS and Android. There are some Cordova plugins that add AdMob to the app, for example this one: https://github.com/floatinghotpot/cordova-admob-pro.
You have to add this as plugin when building VNM game. To do this, you have to open your project, then click Tools > Preferences > Application > Build. Then double click on your desired platform (iOS, Android), add new command line right before the "Building..." and add "cordova plugin add cordova-plugin-admobpro" to the Command Line.
After that you can follow the instruction of this: https://github.com/floatinghotpot/cordova-admob-pro#usage.