As always first step is to download instagram app from play store
Open the instagram app then surf around for videos
Then the next step is to go to file manager>settings>show hidden files
Then open folder android>data>com.instagram>download>files
Note that the files would named as numbers
Click any files and select open with
Use either video player or gallery to open the file
If shown unsupported file format then the file isn't complete
Select files with high size preferably
If the file opens,rename with any name of choice ending it with ".mp4"
Cut nd paste files to any location of choice
Note also that instagram files delete after 24hrs