First of all install full lexmark software on your laptop. During the process you may be asked if you wish to setup up your printer say yes to it. When asked type of connection select wireless.
You may be asked to provide password for the router. The rest is straight forward.
Then reinstall lexmark software on your desktop using usb cable. During the process say no to setup the printer and select you want to add another printer option.For type of connection select network printer.Now remove your usb cable and connect your desktop network cable to your router. Good luck.