In order to perform a two-side printing operation on your Mac computer, you first need to make sure that you have installed the printer's drivers. You can obtain those by visiting the official website of the manufacturer. Also, from the site mentioned you should be able to download the printing utility that is developed to run on Mac and it's compatible with your device. It's advised to use that, because it provides access to all the printer's function. If you are using other tools for printing, check the following website for additional information about two-side printing on a Mac computer.