There is not any free addon for installing Google Tag Manager in PrestaShop except buying a paid addon. Prestashop also doesn’t give entry to Web page code so we are able to add Tag Manager code but there's still an alternate way by directly modifying the web site code on https://addons.prestashop.com/es/seo-posicionamiento-buscadores/30904-etiquetas-automaticas-hreflang-canonical-etiquetas-seo.html