How to Hide Noptin - WordPress Newsletter Plugin Admin Menus

function plt_hide_newsletter_optin_box_menus() {
	//Hide "Noptin".
	remove_menu_page('noptin');
	//Hide "Noptin → Dashboard".
	remove_submenu_page('noptin', 'noptin');
	//Hide "Noptin → Subscription Forms".
	remove_submenu_page('noptin', 'edit.php?post_type=noptin-form');
	//Hide "Noptin → Subscribers".
	remove_submenu_page('noptin', 'noptin-subscribers');
	//Hide "Noptin → Email Campaigns".
	remove_submenu_page('noptin', 'noptin-email-campaigns');
	//Hide "Noptin → Automation Rules".
	remove_submenu_page('noptin', 'noptin-automation-rules');
	//Hide "Noptin → Settings".
	remove_submenu_page('noptin', 'noptin-settings');
	//Hide "Noptin → Tools".
	remove_submenu_page('noptin', 'noptin-tools');
	//Hide "Noptin → Extensions".
	remove_submenu_page('noptin', 'noptin-addons');
	//Hide "Noptin → Documentation".
	remove_submenu_page('noptin', 'https://noptin.com/guide/?utm_medium=Documentation&utm_campaign=Admin%20Menu&utm_term=http%3A%2F%2F127.0.0.1&utm_source=Noptin%20Plugin%20Dashboard');
}

add_action('admin_menu', 'plt_hide_newsletter_optin_box_menus', 101);
Where do I put this code?