In RepU, open your widget, choose light or dark and left or right, then click Copy next to the embed snippet.
In your repository, open _layouts/default.html. If it is missing, copy it from your theme first. Paste your code just before the closing </body> tag.
Need more detail? See the official GitHub Pages guide.
Commit and push. Wait for GitHub Pages to finish building, 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.
Wait for the Pages build to finish. Check your layout file is named exactly _layouts/default.html and that your pages use it.