Itc for2017 -2018 in gst

  i have  doub in gst, gstr 1  return filling  is avablie  31.10.2018  for period July 2017-Mar  2018. gstr 1 return  will be  missed bills and turnover  can be show, how do take itc for missing  purchase   for  period of july 2017-mar 2018 , ( some perosn  said  gst annual  return file by claim refund  for missing purchase itc ) . otherwise we can do  gst3B for month sep  2018 we add missing purchase itc for period july-2017 mar 2018.