Step 1: Login to cPanel and Go to PhpMyAdmin
Step 2: Select Database and Go to wp-options file.
Step 3: Go to Style Sheet and Template, change the theme and save it.
If the theme is still not update in the website, then disable the cache plugins or clear the cache in the WordPress admin panel and re-enable again.
We can also disable the wp-cache entries in the wp-config.php. This will update the theme in the WordPress site.