I had to search this up, click on top right arrow of page right beside your username, click my library in the dropdown box. If you have multiple games on itch.io you might have to scroll down to find buckshot roulette, if not this should be the first game to pop up and you'll press download right below it. From what I can figure out you'll have to download the whole game again but even for my crappy internet service it only takes 30 minutes.
Hope this helps! :)
