So how is the back up labeled? normally an .bak, or .ini . msi?
If you created a settings snapshot (backup) via Edit > Saved Settings > [save] [load] Settings Snapshot, you should be looking for a file named Settings (date).ini and it should be in your MB directory under AppData > Saved Settings > Application.
If you created a layout backup via View > Import/Export > [Export] [Import] Panel Arrangement, you should be looking for a file named with an extension of .layout, and it should be in your MB directory under AppData > Saved Settings > Layouts.
If you created library backups using File > Library > Backup Library the files can be found wherever you saved them when you created the backup. This backup makes copies of the actual files would consist of files named as they are in the MB install directory.