I couldn't find one when I needed to unfollow a mass but I did something that worked. Unfortunately, you'd have to have a spare laptop or not use your laptop at all. It's not the best either but it works... So, here's the method:
1. Download an automatic clicker and keyboard presser (Google it, they're all over the place) and install them.
2. Get on statigram.
3. Go to following.
4. Launch the auto clicker and set it to 25 seconds. Instagram has an unfollow limit by the hour. By setting it to this, it'll be continuous.
5. Launch the auto presser and set it to end every .1 second or something until you've reach a decent amount of people you follow.
6. Go to the top of the page (Home)
7. Start the auto clicker.
8. Place the mouse on the X
Lol, good luck.