There's not any cost-free addon for putting in Google Tag Manager in PrestaShop apart from buying a compensated addon. Prestashop also doesn’t give entry to website code so we could insert Tag Manager code but there's however an alternate way by directly modifying the web site code on hosting server. https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-hreflang-tags-canonical-tags-on-all-pages.html