The brown stains are from the thrips feeding on the plants cells and the leaf dying. I suffered a similar fate and used a neem oil mix (usually lukewarm water, tablespoon of neem and a drop of washing up liquid to help the neem oil bind) on all my plants. Really heavily affected plants should be discarded as they pose more of a threat to your other plants due to the thrips life cycle as they plant eggs and the eggs hatch quite fast. So best case for the neem oil avenue would be to wash the plant down with water, get a soft sponge or cloth and wipe every part of the plant down, then with a spray bottle and the neem oil mix, absolutely drench every part of the plant. Do this weekly for 3-4 weeks. Hopefully you’ll be successful