Unplug the appliance.
Take the top off.
Take the bolts along each upper edge out (note where they fit).
Take the bolts on the rear of the cabinet out.
Take the 2 hidden bolts on the side out.
(bottom centre each side, take out the blanking plug and you'll find the hidden bolts).
Unclip the plastic part at the top rear that carries the water and power in.
You can now pull the rear half of the casing off, giving you full access to refit the belt.
To fit the belt, put it around the motor and onto one side of the pulley.
Cable tie it to the pulley if you can (if not, you need to hold it in place).
Turn the pulley and the belt will stretch itself on.
Hope this helps
Get back to me if you need more help on this.