There's not any absolutely free addon for putting in Google Tag Manager in PrestaShop apart from buying a paid addon. Prestashop also doesn’t give access to Site code so we will increase Tag Manager code but there's however an alternate way by immediately modifying the web site code on internet https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-hreflang-tags-canonical-tags-on-all-pages.html