Originally when I wrote this guide I saw many sources say you do not need to manually erase the firmware when you configure the Duet 2 WiFi for Klipper for the first time. However there's been many cases that has proven false.

With the board powered off place a jumper on the erase pins.

Connect the USB cable from the Duet 2 WiFi to a 5v power source(your PCs USB Port).

Once the diag light comes on remove the jumper

Any firmware saved to the Duet has been erased.