Disconnect the washer from the power outlet.
Move the washer away from the wall slowly. Do not pull it too far away as this might damage the water lines.
Remove the access panel on the lower part of the back of the washer. You may need to remove multiple screws and lift the cover panel off.
Inspect the lower left side of the area behind the access panel. Look for a small 9/16 inch nut near the belt.
Loosen the nut with a wrench. Do not completely remove the nut, simply loosen it.
Tap the motor mounting plate with a hammer to adjust the belt tightness. Tap the plate toward the left for increased tightness.
Push on the center of the belt with your finger to test tightness. The belt should flex about 1/4 inch.
Tighten the nut but do not over tighten it. Replace the back access panel and move the washer back into place. Plug the washer back in.