google app script

function updateForm(){
  // call your form and connect to the drop-down item
  var form = FormApp.openById("Your Form ID");
  var namesList = form.getItemById("The Drop-Down List ID").asListItem();
// identify the sheet where the data resides needed to populate the drop-down
  var ss = SpreadsheetApp.getActive();
  var names = ss.getSheetByName("Name of Sheet in Spreadsheet");
  // grab the values in the first column of the sheet - use 2 to skip header row
  var namesValues = names.getRange(2, 1, names.getMaxRows() - 1).getValues();
  var studentNames = [];
  // convert the array ignoring empty cells
  for(var i = 0; i < namesValues.length; i++)
    if(namesValues[i][0] != "")
      studentNames[i] = namesValues[i][0];
  // populate the drop-down with the array data
  namesList.setChoiceValues(studentNames);
}