What the heck are all of you doing!? You already have the Terminal module! If you installed Webmin using the full package from Webmin.com. If you don’t have it, it’s because you installed the wrong thing (the webmin-minimal package) or you have an old version and you should stop running old software.
If you don’t see it, it’s just because your user doesn’t have access to it. Give your user access to it.
And, stop trying to install weird stuff. Shell In A Box is a very old thing, and there’s a reason (several reasons) it’s not anything we’ve ever distributed as a core part of Webmin or Virtualmin.