I have not done this, but in your situation this is what I would do:
Settings > Maintenance > Use SD
When the B2 reboots, check to make sure that the display says Source: SD. If it says HDD, repeat the Use SD command until success.
USB Menu > Export to C
Plug USB stick into your computer and verify that you got what you expect.
Settings > Maintenance > Use HDD
Again, make sure after reboot the display reports Source: HDD
USB Menu > Import USB C
I'd expect that should get the job done.