How to Hide the "Testimonial Blocks" Admin Menu

function plt_hide_easy_testimonial_blocks_menus() {
	//Hide the "Tools → Testimonial Blocks" menu.
	remove_submenu_page('tools.php', 'etb-blocks');
}

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

Where do I put this code?