Switch back to HFS+ from APFS
I'm afraid there's no non-destructive way to revert back to HFS once converted. You may use diskutil apfs deleteContainer /dev/disk(x)s(x) (where x is your correct APFS container).
This will revert the APFS container back to HFS but will destroy all data. Best find another pool of storage to copy all data from that drive to, then revert, then copy back.