The different settings (Options dialog, Server sets properties) are stored in the "sfo.config.json" file, and the polling history is stored in the "poll-history.sdf" file (SQL Server Compact data file). Both files are located in the in the Simple Failover application data directory - typically: "C:\ProgramData\JH Software\Simple Failover" ("ProgramData" is usually a hidden folder).
To backup: Copy both files.
To restore: Install a fresh copy of Simple Failover and copy the backup files back to their original location.
Restoring settings and data from Simple Failover v. 1.x: Simple Failover v. 2.0 includes a tool "v1.upgrade.exe" which can convert a v. 1.x configuration file (sfo-config.xml) into a v. 2.0 configuration file (sfo.config.json). This tool is found in the directory where Simple Failover v. 2.0 is installed.