The easiest way to achieve this is to use the WP_HOME and WP_SITEURL constants in the site's wp-config.php file, e.g.:
define('WP_HOME', 'https://example.com');
define('WP_SITEURL', 'https://example.com');This will set the correct URLs under Settings > General, and force them to be uneditable via Dashboard. Bear in mind this probably won't change the URLs in the wp_options table in the database. I find the easiest way to change all URLs in a database from http to https is to use WP_CLI, e.g.:
cd var/www/example.com/htdocs
wp search-replace 'http://example.com' 'https://example.com' --dry-run--dry-run does exactly what it says and allows you to double-check what's going to be changed/updated in the database. You might have to append --allow-root to the above command if you're logged in via SSH as root.
I hope this helps.