First of all, you need to install 2 apps on your firestick;
2. ES File Explorer.
PS: When you insall ES File Explorer, dont select FREE TRIAL, just press the back button on remote control.
And then, go to the Settings – My Fire TV – EEVELOPER OPTIONS – ADB Debugging – ON – Apps from Unknown Sources – Turn On
Third, go back to the downloader apps, enter the URL. Such as: iview HD: https://iptvintvbox.com/download/iview-hd-for-stb-download/
If you want to download more apps, enter this URL: https://iptvintvbox.com/download/