It looks as though there might be something causing that area to raise up. I would file it down with a nail file to get to the fresh scute material underneath so it can heal and not get worse. If you don't feel comfortable doing it, take the tortoise to a reptile vet in your area and have them clean it up for you.. They might be able to clean it up and also give you some antibiotic ointment to put on it if they feel it is necessary.I was taking a close look at my 2 year old marginated tortoise and noticed a spot on his she'll was a little raised in a corner compared to other places. Is that something to worry about? Im afraid it'll flake off or something.
It looks as though there might be something causing that area to raise up. I would file it down with a nail file to get to the fresh scute material underneath so it can heal and not get worse. If you don't feel comfortable doing it, take the tortoise to a reptile vet in your area and have them clean it up for you.. They might be able to clean it up and also give you some antibiotic ointment to put on it if they feel it is necessary.
On another note, the shell looks rather dry in your photo. Do you soak that tortoise daily or not?