This is really easy to do on Android, but if you’re using an iPhone the process can be a little tricky. Go to the Google Drive link and click the “…” settings button in the top right, then choose “Open in” (the icon looks like a D-pad with four arrows). The video will export and then a menu will appear with an option that says “Save to Files”, click that button and save the clip in the “On This iPhone” directory. Then go to the Files app on your phone, open the video clip and then click the button in the bottom-left corner (a box with an arrow pointing upwards) and select the option that says “Save Video” (a box with an arrow pointing downward). This will add the video clip to your Camera Roll and you’ll be able to post it to Instagram. I hope this helps!