If you have already added the files correctly (and the error would seem to imply that you have) then you need only add the tables.

However, there's a catch. By adding the files you prevent yourself from accessing the Zen Cart feature to add run the SQL that adds the tables. So it would need to be done by hand with your database prefix edited into the SQL by hand and then it being run via a third party app such as phpMyAdmin.

I have the impression that might not be something with which you're comfortable - in which case removing the files and re-installing using the installation instructions would be a better option.