code: @UiThread
      public void rebindIfNeeded() {
          ThreadUtils.ensureMainThread();
  
          Iterator<RouterTransaction> backstackIterator = backstack.reverseIterator();
          while (backstackIterator.hasNext()) {
              RouterTransaction transaction = backstackIterator.next();
  
              if (transaction.controller.getNeedsAttach()) {
                  performControllerChange(transaction, null, true, new SimpleSwapChangeHandler(false));
              } else {
                  setControllerRouter(transaction.controller);
              }
          }
      }
docs: Attaches this Router's existing backstack to its container if one exists.