If statement with row by row

I'm a newbie in coding, and I have limited knowledge in English. Sorry for that. Here is an example of a code that I'm using.

   function () { 
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var em = spreadsheet.getSheetByName("E_M");
  var db = spreadsheet.getSheetByName("db");
  em.activate();
  
  var checkbox = "j6"
  var target = em.getRange('n6').getValues();
  var base = '\'E_M\'!k6:l6'

  db.activate();
  spreadsheet.getRange(target).activate();
  spreadsheet.getRange(base).copyTo(spreadsheet.getActiveRange(), SpreadsheetApp.CopyPasteType.PASTE_VALUES, false);
  
  
  
  db.hideSheet();
  em.activate();
  
  }

It's a basic database and this section is for adding a data block. This code is for 1 row only. I have 60 rows to check. I'm using check boxes in j column and N column has the address cell number in it. I need is if the j is true than copy K:L into the cell numbered in N and do it for 60 rows. Sorry for my English and thank you for your help.