Hi Febria,
Please follow the steps below to update the theme and plugin.
1. Go to Appearance -> Themes
2. Active another theme & delete the cvit
theme
3. Click Add New -> Upload Theme
4. Upload, install & activate the latest version of cvit
theme
5. After then, deactivate and delete the “cvit-core” Plugin
6. install & activate again the “cvit-core” Plugin from the Appearance -> Install Plugins
Or check out the article https://www.wpbeginner.com/wp-themes/how-to-update-a-wordpress-theme-without-losing-customization/
Moreover, you could try Envato Market Plugin http://envato.github.io/wp-envato-market/ for automatic update.
***(need to remove and reinstall the “cvit” Theme and “cvit-core” Plugin to get the above updates)***
Best Regards,
ThemeLooks Support Team