How to Hide WP SMTP Mailer Admin Menus

function plt_hide_wp_smtp_mailer_menus() {
	//Hide "WP SMTP Mailer".
	remove_menu_page('wp-smtp-mailer');
	//Hide "WP SMTP Mailer → WP SMTP Mailer".
	remove_submenu_page('wp-smtp-mailer', 'wp-smtp-mailer');
	//Hide "WP SMTP Mailer → SMTP Settings".
	remove_submenu_page('wp-smtp-mailer', 'smtp-settings');
	//Hide "WP SMTP Mailer → Test Email".
	remove_submenu_page('wp-smtp-mailer', 'smtp-test-email');
	//Hide "WP SMTP Mailer → Email Logs".
	remove_submenu_page('wp-smtp-mailer', 'smtp-email-log');
}

add_action('admin_menu', 'plt_hide_wp_smtp_mailer_menus', 11);

Where do I put this code?