WPBakery's Page Builder plugin comes free with the theme. The license activation option in the plugin is hidden when Shopkeeper is activated and that prevents free users to be asked for license activation at all times, but if you do have your own license and would like to activate it to unlock their premium library and automatic update, you'll have to temporarily deactivate the theme. You can do that by enabling the default WordPress theme, TwentySeventeen for example. As soon as Shopkeeper is deactivated you will be prompted to activate the plugin's license and the License Activation section will no longer be hidden.

You can go back to Appearance > Themes to activate Shopkeeper back as soon as you're done with the plugin's License Activation.