Reformat is not master reset nor does “remove files”. Reformat does what the name says: reformats the unit, thus erasing EVERYTHING on the unit, even installed packages (yes, that includes the OS, maps, rwdata partition)… unit won’t be operative again until the reformat phase is completed
Going back to an older Sync3 version is required since the reformat tool has been blacklisted in most 3.4 builds
You need to reformat the unit in order to erase the rwdata partition… this is actually a “half-true” statement, since you are not just deleting the rwdata partition, you are starting everything from scratch.
Once you manage to downgrade to another build where the reformat tool is permitted, you should be good to go to fully reformat your unit with the desired version.