If you want to install this app on Firestick , use this step by step guide:
- Click on the Settings from the main menu.
 - After that, click on the My Fire TV or Device option.
 - After that, click on the Developer Options in Device.
 - After that, click on the Apps from Unknown Sources option.
 - After that, click on the Turn On button.
 - Return to the Home Screen and click on the search icon.
 - Type “Downloader” in the search box.
 - Click on the Downloader app and install it.
 - Click on the Open button.
 - Click on the Allow button.
 - Click on the OK button.
 - After that, visit Settings in the Downloader app from left.
 - Click on the box front of Enable JavaScript.
 - Click on the Browser or Home.
 - Click on the URL bar.
 - After that, click on the URL to download Duplex IPTV Player APK. (https://bit.ly/dpxplay)
 - Now the APK file is downloading, so wait for a few seconds.
 - Click on the Next button.
 - Click on the Install button.
 - Wait for installation.
 - Click on the Done button.
 - Click on the Delete button.
 - Click again on the Delete button.
 - Click on the Home button on your remote, you will get the following screen then click on Apps.
 - You can see Duplex IPTV Player is located at the bottom.
 - Select Duplex IPTV Player and long press on the menu button on your Firestick remote, you will get options on which to click on the “Move to front” section.
 - Now launch the app.
 
Download Link is available here https://bit.ly/dpxplay
if you want to watch a video of duplex play setup you can use this link  
https://www.youtube.com/watch?v=WroJuS8C4qY
