You can still access the left navigation(see the screenshot), even you check the 'Hide left navigation' option from the [preferences][1] tab
[![enter image description here][2]][2]

Expanded Menu:
[![enter image description here][3]][3]


  [1]: https://drupal.stackexchange.com/users/preferences
  [2]: https://i.sstatic.net/ny9id.png
  [3]: https://i.sstatic.net/Tapml.png