Unplug the washing machine if it's plugged in. Turn off both the hot and cold water supply valves by turning them all the way to the right.
Insert a putty knife between the top of the machine and the cabinet at the front corner of the machine. Gently wiggle the putty knife until you feel the spring clip beneath unlatch. Do the same for the opposite front corner. Lift up the top of the machine so you can access the tub.
Slip the washing machine drum over the agitator shaft in the middle of the washer tub.
Thread the spanner nut over the agitator shaft and hand-tighten it.
Slide the spanner wrench over the spanner nut until it locks into place.
Hold the drum with one hand. With your other hand, tighten the spanner wrench clockwise as far as it will go. Tap the end of the wrench with a hammer a couple of times to lock the nut in place.