You can set the permissions on the file using your FTP program. Most of them allow that sort of thing.
Basically (depending on your FTP program) you select your remote file (in this case, your PL file), then right-click to get a context-sensitive menu and choose "Permissions..." Some FTP clients have other ways of implementing that function, such as a button, or so forth.
You want to be sure that your Perl script is executable by anyone and everyone.
You might also want to look at the CGI-BIN directory itself and make sure its permissions are similarly set.