HyperCon is a graphical application which allows you to configure Hyperion (an ambient lighting system) running on a remote LibreELEC device, from a Windows, macOS or Linux desktop. Hypercon is a Java application, and so requires you to have a working Java runtime environment (JRE) installed to run it. Java v1.7 or higher is required.
Download and install the correct 32-bit or 64-bit Java Runtime for your Windows OS version from the official Java download site https://www.java.com/. Open the .jar file as you would a regular .exe file and it should launch using Java (JRE). If not, right click and select “Open with” then “Java” listed in the list.