Brother DCP-7057 Service Manual page 259

The Printers window appears as shown below.
2) Right-click the Brother Maintenance USB Printer icon.
3) Click Properties.
The Brother Maintenance USB Printer Properties window appears as shown below.
4) Click the Ports tab.
In this example, the port number assigned to the Brother Maintenance USB Printer is
USB001.
(5) Enter the serial number (the fifteen digits) of the machine into the box on the "Serial No".
(6) Click the [OK] button. The serial number is written in the machine.
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