If your server has no access to the internet, then you'll need to solve both of its problem domains manually:
- Knowing what plugins are available, and which versions are appropriate for your server.
- Obtaining and installing new plugin versions.
For the first, you must use the plugin version matrix, which is kept up to date with plugin availability and compatibility.
For the second, simply download the new plugin an place it in [sonarqube-home]/extensions/downloads and restart the server.
perform your plugin upgrades manually.