How to avoid stretching foreskin?

I’m a complete newbie at this and I’m very skeptical about the ability gain length and girth through exercises, but the explanations sound reasonable so I’m gonna give this a try..

However, the only thing that scares me is that I’m uncircumcised and I wonder if any jelqing is going to just stretch my foreskin instead of the actual member?

Also, how do I use cock rings?