Disconnect the wire terminal from the "negative" terminal of the battery.
For clarity, the operation is shown with the heater fan removed.
We disconnect the block of the wiring harness, with a Phillips screwdriver or a "7" head, we unscrew the two self-tapping screws for fastening the resistor..
... and remove the resistor from the heater housing.
We install an additional heater fan resistor in reverse order.