There’s no way to grind scratches off the actual glass part of a camera lens, this had to be either the lens coating or just the UV filter. Besides, how do you scratch the lens behind the filter? People should not try this if they don’t know a filter for the lens.
Always, if the actual lens does get dirty. try using a dry air bulb to clean the actual lens first, then only try a real reputable camera manufacturer’s lens cleaning paper or cloth only (Hasselblad, Nikon, Minolta, etc.). If the lens is scratched, leave it alone and try it out. You may find that it works ok still, or there may be some clouding if its bad enough and the sun hits it. Don’t try rubbing (grinding) out the scratch yourself. As mentioned above, you can rub off the lens coating and get glare, or worse, make the glass get frosted, which will render your optics useless by rubbing them with coarse compounds! If it’s a bad enough scratch, you might have to just replace it.
I’m sure OP is either talking about the Hasselblad UV filter, or is actually rubbing off the lens coating. But be aware that the filter is also coated and you can get backscatter reflections if you rub that off from the back side of the filter.
