1) From the Home screen please go to My Fire TV -> Developer options -> and set the parameter Apps from unknown source to On

2) Install the Downloader app from the Amazon app store.

3) Run the Downloader app, switch to the Browser inside of the Downloader app and open the following web page https://trustedzone.info/de/client_android.

4) Download the Trust.Zone_VPN_Client_vXX_bXX.apk file and run it to install.

5) After the installation of the Trust.Zone VPN Client is complete please hold the Home button on the remote control for a few seconds then click on Apps to see the list of apps installed on the device.
Trust.Zone VPN Client may appear as the latest app in the list (green android icon). After first run of the app you will be able to run it from the recent apps section from the Home screen.