Could you be more specific please, what is your OS? the word version? That printing option is usually black out or it's manual. Here are
few things you could try anyway for printing on both sides.
Go to 'Start' - devices and printers, then by right clicking the printer go to 'printer properties'- device setting - (click the + sign if necessary ) then 'installable options' - Duplex Unit and click Installed - Apply and then OK.
again Go to 'Start' - devices and printers, then by right clicking your printer icon go to
'printer preferences' this time - Click features, then 'paper saving option' change it to
Automatic from the two sided printing option - OK
Try all these and let me know, thanks...