They should have demanded unconditional surrender and marched on Berlin. This would be followed by a period of full occupation where the country would be reorganised.Everyone agrees that the Peace that came at the End of World War One, specifically the Treaty of Versailles, was flawed from almost the beginning and set the stage for World War II and the rise of Nazi Germany.
So what should the United States, Britain, and France have done differently regarding Germany at the End of World War One? Should they have pushed the Germans back into Germany, and take the fight to Berlin? What about the Russian Civil War?
The leaders could have been sent off to live in exile.
This would kill any chance of the stabbed in the back myth. The new government and constitution would be agreed amongst the Entente powers with the borders of Europe being similar to what they were IOTL.
The biggest issue is reparations though and I don't think there is a good answer although the Germans bore the war guilt.