aptitudetest.js

function myFunction() {
  // Get all rows in the sheet minus the first
  var rows = SpreadsheetApp.getActiveSheet().getDataRange();
  var data = rows.getValues();
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();

  for (var row = 2; row < data.length +1; row++) {
    for (var col = 3; col <= data[row].length; col++) {
      let cell = sheet.getRange(row, col);
      let cellData = cell.getValues()[0][0];
      if(cellData.length > 2){
      cell.setValue(cellData.charAt(1).toUpperCase());
      Logger.log(cellData.charAt(1).toUpperCase())
      }
    }
  }
}