How do you replace fiat punto windscreen wiper control unit?

I'm guessing you mean the front wiper here,- you just remove the cover over the nut and unscrew using spanner. make sure its not too loose or it will come off during motion. that's as far as i can help.

THE WIPER CONTROL UNIT IS UNDER THE BLACK PANEL UNDER THE WIPERS,, TAKE OFF WIPERS AND BLACK PLASTIC PANEL CONTROL UNIT UNDERNEATH,,,,