Digestion takes place in the stomach and in the intestines, not in the liver. The main responsibility delegated to your liver in terms of digestion is the production of bile salts and cholesterol required to emulsify the fats that you ate for breakdown by pancreatic lipase and subsequent absorption by the small intestine. Please specify what you mean by a "weak" liver. Do you have cirrhosis? Hepatitis? Fatty liver disease? There is no solution that can be provided until you specify the details of the problem.