Part 2 should not have been required there.
In order to downgrade, you should first install any application firmware targeted at your system to be - to prevent an accidental OTA update in the process.
Next system part 3 (for Electron only), part 2 & part 1.
If you then still find your device in DFU Mode, you need another application firmware flash (e.g. particle flash --usb tinker, or your previous application).
After that you probably also want to flash the bootloader that belongs to that version via particle flash --serial bootloader-<....>.bin.