SyncBackPro, SyncBackSE and SyncBackFree are available via the Windows Package Manager winget. To install winget in Windows, refer to Microsoft's documentation. For simplicity, only the 64-bit version of SyncBackPro and SyncBackSE is available via winget. Also, the installer is the elevated one that requires you to be a Windows administrator.
To see which old versions of SyncBack are available, go to the Windows command prompt and type:
winget show 2BrightSparks.SyncBackPro --versions
The above shows all the versions of SyncBackPro available via winget. Change the command as appropriate for SyncBackSE or SyncBackFree to see versions for those.
To install an old version:
winget install 2BrightSparks.SyncBackPro --version 10.2.129.0
The above example will install SyncBackPro V10.2.129.0