How to keep a healthy shell?

[Turtle001]

So I recently purchased my first Russian tortoise named Herbert. I love him so much but I don't think he was cared for well at petco his shell is very worn down and I really want to keep him healthy, how can a build it back up? (By the way, this isn't his enclosure im currently soaking him. When I first got him he was never soaked and all of his skin was caked in dirt and food.)
Here are some photos

 

[Yvonne G]

If I'm interpreting your picture correctly, actually, that is a very healthy-looking shell. I THINK (and I can only guess from years of experience) that at one time a while ago this tortoise was chewed by a dog or other sharp-toothed animal, and all the keratin was scraped off, exposing the bone. The bone died and after many, many months, popped off, leaving you with the beautiful, new keratin that you are seeing on the tortoise. The new keratin never looks like what the old keratin looked like, but to me this looks just fine. There are still a few rough spots, but overall, I think it looks fine.

This might be a case of a tortoise benefiting from the use of a good occasional polish with Extra Virgin, Cold Pressed coconut oil. Put on a tiny amount and rub it in, leaving it on for 15 or 20 minutes to soak in, then polish it all off with a clean absorbent cloth.

Just as in human hair and fingernails, a good diet is what makes your tortoise have a healthy shell.