I just contact with the garage guy, he said he mean to remove it because it is secured by the rivet that is same as the wheel arch. And it is easy to get loose if you don't use the new rivet. But I told him mine was fell off to the bottom. Well, will check next Monday.
But he said there are 2 guard plates, one top and one bottom. Also, MK1 don't even have it. And actually, most japanese car don't have the guard plate too.