Oh, I did it twice but it didn't work. Actually I was one of instagram users but I uninstalled it without deleting my account, and now I just want to go back to my account so that I tried different ways to reinstall it but nothing helped. For example I used Google play over and over but it was just warning that this app is not compatible with my device or isn't available in my country!!Look on APKMirror.com for older versions of the Instagram app, download a copy of the APK file from there and install it using a file manager. The current version requires a version of Android later than the one you have on your device, which is why you can't install it.
I'm sure I did, but I opened the link above, tried to download its apk file and reinstall it, and again it warned me the app not installed.Instagram 7.2.2 (13167125) (arm) (320dpi) APK Download by Instagram - APKMirror
You didn't do it at all, because I found the above link in about thirty seconds of searching. You must download the file from the link above and install it using a file manager, because you cannot use the Play Store. The current version of Instagram on the Play Store requires a newer version of Android than what is on your tablet. Thus the version on the Play Store will always refuse to install.