It should default to the program directory where BI is installed, ie, C:\Program Files\
Blue Iris 5
From the BI Help File:
BAC K U P S
Software Settings
Options to Export and Import software settings may be found on the About page in
Settings. The complete software settings reside within a .REG registry keys file and may
also be found via REGEDIT at the key
HKEY_LOCAL_MACHINE\SOFTWARE\Perspective Software\Blue Iris
If you select the Auto export option, you may select a folder location for these files. The
software maintains a rolling set of three files, always from three different days. These are
updated only when the software service is restarted. Restarting the software multiple times
on a single day results only in the replacement of just one of the backup files.