In fact, it is not so complicated to clean sunglasses. You can just clean your sunglasses with tap water and dry it with a pieces of soft cloth ( usually, you will get a special sunglasses cloth when you buy sunglasses). If the tap water can't clean the sunglasses, you can just use water mixted mild soap to rub you sunglasses till it clean. Then use tap water watch it again. Hope this help.
You can just wash it with the clean water. If there is oil on it, you may use the abluent to wash it. Just use your fingers to wash it and at last use the clean cloth to rub it. Keep in mind that d not use the toothpaste to wash it which may easily scratch the sunglasses.