Buy new belt....Assuming the old one is damaged. Ensure washing machine is empty of water. Unplug washing machine. Tilt it upwards. Support it with something solid. If it falls on you it will hurt you to say the least. Wrap new belt around the 3 pulleys. (2 small and one big) You may have to turn the last pulley as you are putting on the belt. Lower washing machine, and you are in business.