In RepU, open your widget and click Copy next to the embed snippet.
In WordPress, go to Plugins, then Add Plugin, and install and activate WPCode. Open Code Snippets, then Header & Footer, and paste your code into the Footer box.
Click Save Changes, then open your live site to see your Google reviews.
Check your live site in a private window, not the WordPress editor. A domain-locked widget only shows on your own domain.
If your site uses caching, clear the cache, then check again.
On WordPress.com, plugins need a paid plan. If you are on the free plan, upgrade, then check again.