In RepU, open your widget, choose light or dark and left or right, then click Copy next to the embed snippet.
Open layouts/baseof.html, or layouts/_default/baseof.html in older themes. If it lives in your theme, copy it into your own layouts folder first. Paste your code just before the closing </body> tag.
Rebuild your site and deploy it, 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 your own copy of baseof.html, not the theme original, and rebuilt the site.