The File or Folder class in Google Scripts offers no direct method to move files from one folder in Google Drive to another. You do have an option to add files to multiple folders and we can use the same technique to move files across folders.

function moveFiles(source_folder, dest_folder) {
  var files = source_folder.getFiles();

  while (files.hasNext()) {
    var file = files.next();
    dest_folder.addFile(file);
    source_folder.removeFile(file);
  }
}

Alternatively, you can copy a to another folder, set its name to the original file and then trash the original using the setTrashed(true) method of File. This method will however fail if the files have been uploaded by another user while the script is running under a different user.

function copyFilesAndTrash(source_folder, dest_folder) {
  var files = source_folder.getFiles();

  while (files.hasNext()) {
    var file = files.next();
    file.makeCopy(target).setName(file.getName());
    file.setTrashed(true);
  }
}