Since Apple released itubes 12.7 they removed both App management and Ring Ztone management from itunes completely. Well because of complaints Apple has now released iTunes 12.6.3 which features app management, of course once you install it you will no longer get notices for new versions of iTunes and it will eventually break.
Apple should just admit they were wrong and either put the functionskity back or make a new app that has just iOS management.