Due to the way Bubble websites/apps are built, you can't install widgets to appear across your entire website from one code installation. You can only install widgets on a per page basis.
1.
Log into your Bubble account and from the main dashboard, select the app you want to add the widget to.
2.
Within the side menu, select Design and then drag the </> HTML element onto the desired position on the page.
3.
Once in the desired position, copy the Widg.io Element Script and the Installation Code and paste it into the HTML Appearance Editor. Publish the changes.
You have now successfully added the widget to this page.