On your Instagram page, point at the timestamp at the bottom of the post and 'Right click', click on Copy Link Address. See screenshot below.
Go to IgDownloader.net. Then paste the URL and Click 'Download', like the screenshot below
Click on Download Video or Download Photo (if this post is photo) to start download.
Note: If the video starts playing instead of downloading, then on Step 3 Right Click the link and "Save as..." to download the video.
Open the Instagram app and Tab to Top Menu on any post on your feed or timeline, then Tap Copy Link.
Open Web Browser (Safari or Chrome), go to IgDownloader.net, and Paste the Video Link before tapping Download.
Tap and Hold on Download Video or Download Photo then confirm the download.
Note 1:You can find your downloaded videos under the 'Downloads' section in Chrome/Safari menu.