The Volca FM can directly import sysex files that contain patches from the Yamaha DX7. This process works the same as importing any other patch file into Patch Base.
However, when you import a patch from the DX7, some operators may be turned off; this is a result of a slight difference between the DX7 and the Volca FM. So, after importing a DX7 patch, you should tap the "On" box for any of the 6 operators in the editor that are turned off, to ensure the sound matches the original from the DX7.
For more resources related to this synth, read our Korg Volca FM Resources page.