Step : download the free insta tv app used to download used to download the video on instagram.
Step 2 : using your user name and password log into instagram , on the instagram app.
Step 3 : tap on your timeline. You will then see all the latest photos and videos in your instagram feed. Swipe right to left to navigate the video you need to download.
Step 4 : tap on the save icon at the bottom right corner of the screen , and the video will be automatically saved to your library.
Step 5 : note that you will first have to grant the app access to your video library. The video will then download to your camera roll.