"cpan install" trying to use /sw/bin/tar (instead of /usr/bin/tar)

I'm having no luck getting CPAN modules to install on my M1 Mac running Big Sur. They all seem to be trying to use /sw/bin/tar to untar the archives, but there is nothing there; tar is in /usr/bin/tar. Mac OS does *not* want me to create anything like /sw, so I can't create a link to it there or anything. The two modules I'm trying right now are GD and Imager, no luck on either. Who knows what additional problems I'll run into after this is solved, but right now I can't get past this point.