Unplug the washing machine's power cord from the wall outlet.
Grip the metal U-shaped clip behind the existing start knob with a pair of needle-nose pliers. The clip is between the back of the knob and the front of the control panel.
Pull the clip off the shaft of the control knob to slide off the knob.
Slide the U-shaped clip back into the groove on the shaft that held the knob.
Align the D-shaped opening on the back of the new knob with the shaft and push it in place until it clicks.