Yeah.Scratches on plastic sunglasses can be repaired by applying Armor Etch. So firstly put a small amount of Armor Etch onto each side of the lens. Wait for five minutes. Rinse and wipe lens dry. This way only can repair the minor scratches.Replace your lenses if you have major cratches.
There is coating on sunglasses. Maybe you will remove the coating as well. But if a pair of sunglasses can't block harmful UV rays for your eyes. Why not buy a pair of new sunglasses. There is sunglasses case to store the sunglasses. So your sunglasses won't get damaged as long as you put them in the case when you don't need them. This can avoid get some scratches on the lenses and break them by accident.
We can just remove mild scratches from our lenses. As to the deep lenses, there is no way to get rid of them. If you just have mild scratches on your lenses, you can buy a kind of cleanser from a nearby optician. The optician knows which kind of cleanser you want. But the cleanser will remove the coating as well, so your sunglasses can't block harmful UV rays any more. If you have deep scratches on your lenses, you'd better buy a pair of new sunglasses.