To know about the steps to smoothly then you need to connect it through USB cable. For this, connect your USB cable from PC to mobile phone. Now, wait for PC to recognize your phone. Proceed the file on computer and copy the downloaded media. Now, proceed to phone and go to file manager or folder. From there, you need to paste the media to save it on phone. Lastly, you need to open the Instagram account to upload the video
To see this working, head to your live site.