Write a patch that fixes the open bugs, and the bugs you've found.
Submit that patch to the listed author, copying the modules mailing list in your e-mail.
If the author accepts that patch...
Your work here is complete!
Elsif the author says he is no longer interested in maintaining the distribution:
Ask if you can take over as maintainer, and if he agrees ask him to inform the Perl modules mailing list.
Someone on the mailing list should be able to give you the permissions on CPAN to take over the module.
Release a new fixed version.
Elsif you get no reply after a couple of months:
Explain the situation on the Perl modules mailing list, including what you have done to contact the author. Ask tobe made the maintainer of the module.
Someone on the mailing list should be able to give you the permissions on CPAN to take over the module.