How to share IGTV Preview in Stories - New Instagram Update
Instagram users can now share their favorite IGTV videos to their Instagram Stories.
This could be done with your own IGTV videos as well. In the November 2018 update, you can simply click the airplane icon on an IGTV video and share it on your own story.
It will create a preview inside Instagram story that anyone can click and watch the entire video on IGTV.