While the text implies this is a slam dunk easy as pie firmware update it is not!
You need a second system which is running the special tool code connected to your Mac via an internal connector which needs to be soldered on!
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Unless your system has been in a drawer it’s likely by now it would have failed by now.
After checking the systems S/N if it was in need I would still make an appointment with the nearest Apple Store or ship it to Apple for repair.