Open your dashboard: https://commbox.glbth.com/index.html#/dashboard, on the left side menu, click on repositories, open up policies and select add new.
Name the policy and select blocklist from the left hand side. Select block list from the drop down menu and add all apps that you don't want accessible by pressing the '+'.
Now you can add your new policy by selecting 'device' or 'group' from the left side. Click on the 3 dots and select policies.
Here you will be apply to select your new policy and hit 'Apply'. This action is almost instantaneous, all devices need to be connected to the network for this to work.