Resumes a file iteration using a continuation token from a previous iterator

Question

I have several Forms in a folder in Google Drive. I want to open each form and edit them, that is, delete old items and add new items. I used the following script code:

function myFunction() {
var files = DriveApp.getFolderById('1qKvLqpqvdBLVHIElOvBT-iIm8NxTCeTt').getFilesByType(MimeType.GOOGLE_FORMS);
while (files.hasNext()) {
  var file = files.next();
  var formId = file.getId();
  var form = FormApp.openById(formId).setTitle('abc');
  for(var j = form.getItems().length - 1;j>=0;j--){
      form.deleteItem(j);
  }
      for(var i = 1;i<=50;i++){
      form.addDateItem()[i];
      }
     }
}

However my runtime exceeded the 6 minute limit. Do I know DriveApp.continueFileIterator can help my script code keep running, but I don't know how to use it. Can anyone help me, thank you.