The widget is found in the Reviews.io dashboard, under Company Reviews >> Publishing. Full installation instructions are found there, but here's an overview of the customisation features available to you:
You can change everything from the background colour or the border style, right through to the number of review cards in the widget and which review types appear.
On top of all the options in this table, you can also edit the widget code directly, which opens up a whole raft of other customisations.
To see the rest of the widgets in our library, log in to your dash or visit the Widget Library page on our website.