Hello,
Thank you very much for choosing our theme and for contacting us.
WPBakery Page Builder and Revolution slider come bundled with our theme but they can’t be activated with our purchase code. Actually, you don’t need to do this. Only in case you want to get free premium support from its author, you can purchase it from Codecanyon. But it is not necessary since we will always provide you with the latest updates.
In order to update the plugin, navigate t to Appearance > Install Plugins. If you cannot, upload the plugin from this forum profile and install via Dashboard > Plugins.
As for the second problem.
Please deactivate all the plugins not related to the theme and switch the parent theme, check the issue, if the problem remains, leave the plugins not activated and provide the site admin access to the private area
Best Regards