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Go to this website --> http://support.brother.com/g/b/downloadlist.aspx?c=us&lang=en&prod=mfcj870dw_us_eu_as&os=10018
Then download and install the following
After downloading and installing both, download the Wireless Setup Wizard and open it to connect the printer to your Mac.
(If you want to see your downloads file, then click on Finder icon on dock, click on GO menu at the top bar and select Downloads. This will bring Downloads folder and you will see downloaded files there).
You can also add the printer from Apple > System Preferences > Printers and Scanners.
If you have any difficulty on following the steps above, please let me know and I will continue to help you