How to print to printer connected to Windows 7 PC from iPad Air?
The L7590 does not provide Airprint capabilities and can 't be added.

If you run Windows you can try to enable AirPrint - like described here (I haven't tried it my self, because I'm running OS X, so I can't comment on how good it is): http://www.airprintactivation.com/ - then the printer(s) setup on your PC will be available in iOS

If you run OS X you can download a more less free AirPrint enabler: http://www.netputing.com/handyprint/ - then the printer(s) setup on your Mac will be available in iOS