In RepU, open your widget, choose light or dark and left or right, then click Copy next to the embed snippet.
Open the Twig layout your templates extend, often templates/_layout.twig. Paste your code just before the closing </body> tag.
Deploy your updated template, then open your live site to see your Google reviews.
Check your live site in a private window, not the editor or preview. A domain-locked widget only shows on your own domain.
Make sure you edited the layout your templates extend, and clear the Craft template caches after deploying.