Make a paste from some baking soda and water. Put some of the paste on your lens and rub it with a cotton or wool cloth in a circular motion. Rinse it off with cold water and wipe it dry. You may have to repeat to fully remove the scratch.
There is a product called Armor Etch, which is a glass etching compound, that could be used to resurface your plastic lenses and remove scratches. NEVER USE THIS REMEDY ON GLASS LENSES, plastic only!
Paint a thick coating of Armor Etch onto each side of the lenses and let it sit for five minutes, then rinse and wipe dry. Make sure you don’t rub the compound into the lenses. Armor Etch will get rid of the outer coating and the scratches that were on it.
You can also use car wax to get scratches out by applying some to your lens with a soft clean cloth and gently buffing the scratch away.
Windshield Water Repellent
Apply some windshield water repellent with a cloth and gently rub it in for a few seconds. This works best on superficial marks and will also help to repel dirt, moisture, and will prevent your glasses from fogging up.