How to add back button for specific content?
Duplicate your node.tpl.php file (in your theme's folder) and rename it to node--[content type].tpl.php. Use machine name of the content type, which can be found in Administer > Structure > Content Types
Replace content type with name of your content type. (i.e for page content type, node--page.tpl.php)

Don't forget to flush all caches when you have placed the new code in this new template.

Drupal will now use this custom template file for this node type, and the node.tpl.php base template for other types.