Hi Oscar,
Thank you for reaching out. Please be advised that you do not need to register Revolution Slider extension since this is a bundled plugin. We will be the ones who will be providing the updates of this plugin so you can simply ignore the notice.
We’ve mentioned this here https://theme.co/apex/forum/t/extension-revolution-slider/71 as well:
there is no need to register your license for Revolution Slider if you happen to have one. In fact, doing so is discouraged in order to prevent any potential conflicts when updating, as previously mentioned. If you happen to see a notification in your WordPress admin panel asking you to register Revolution Slider upon activation, simply dismiss this notice.
Since the creators of the plugin launched Slider Revolution 5.0, they have removed the template import. It is now exclusively available if you have purchased a separate license for the plugin. For bundled plugins like what you have do not have any more access to the templates. It is the creators of the plugin who made this change in their policy. We at Themeco do not have any control over their policy changes.
In addition to that, the warnings are displaying because your debug mode is turned ON. To get rid of the PHP notices and warnings, please disable the debug mode. You can do this by opening wp-config.php and adding
define('WP_DEBUG', false);
/* That's all, stop editing! Happy blogging. */
When you revisit the page, you should no longer be seeing those warnings. You can also refer to the following guide https://www.wpbeginner.com/wp-tutorials/how-to-turn-off-php-errors-in-wordpress/
Hope this helps!