The app is currently deployed on a (open source) Shiny Server on a DigitalOcean machine at http://165.227.11.103/
The actual code for the app lives at /srv/shiny-server/ssi_calculator/. That folder is a clone of this git repo, so to update the application you can do a git pull from within that folder. Note that if you manually modify files in that folder and then try to do a git pull, you will likely run into merge conflicts, so it's a good idea to only pull from that serer and not develop on it.