An ETS App is a functionality extension, i.e. it adds functionality to ETS5. In order to add this functionality in ETS5, a binary file ('.etsapp') shall be installed in ETS5. To make this happen, please follow the steps below:
1. Visit MyKNX and sign-in in your account. Go to 'My account-->My Products' section.
2. Find the ETS5 App license that you have previously bought, under the 'Licenses' section and then click the green 'Download' button to download the 'etsapp' file, which will add functionality in your ETS5.
3. Start your ETS5; Click on the item 'Apps' to open the App list window. Then click the icon on top to locate and install the '.etsapp' file.
4.Locate the license file, select it and then press 'Open' button. Your ETS App is now installed! You will see the new entry appearing in the list of available Apps.
To license the ETS App, see here.