Unfortunately the build in file system repair tool that can be used from DSS V6 console works only for XFS file system which is used on NAS logical volumes. There is no vfat file system verification/repair tool in DSS V6.

As workaround you can prepare a new USB memory stick with a trial version of DSS V6.
Download the 'Setup' and 'Configuration' from DSS V6 webgui -> MAINTENANCE -> miscellaneous and save them locally on a host. Now you can unplug the old DSS V6 USB stick and boot your server from the new stick and import the settings.

BR,
Tomek