Adding canonical tag in html is going nowhere

It goes in the head, one per page: Use the full absolute url with https and the same trailing slash/www version you actually serve. If you're on wordpress, don't hand-edit it, your seo plugin already outputs one and you'll end up with two. How long: google picks it up on the next crawl, but it's a hint, not an order. If the page it points to is a near duplicate, give it a few weeks. Check it in URL inspection, it shows "google-selected canonical".