The belt while mowing snapped in half. I do not have the owners manual since the mower is over 20 years old. Please help

20 years and still going. "Nothing Runs Like a Deere" You are talking of the deck belt? Although I do not have a diagram I can tell you how a belt routes. The outside of the belt will go against the flat pulley and the inside or notched side will go in to the notched pulley. And of course it will go around engine pulley. Hope this helps. Knowing how belt goes may help you a little. Good Luck