Youtube downloading is not supported anymore.
Open your instagram app and tap on the options icon of any video that you want to download.
An overlay dialog appears at the bottom of the screen promting you to download the video you have chosen. Tap on the download button.
Once resolution is selected a dialog appears which allows you to change your download location and select number of network threads for fast downloading.
Tap on download button and your download begins. You can tap on the download icon on the top of the screen to view your downloads.