Google Tag Manager (GTM) is an amazing tool for your website. If you don't have it installed, we highly recommend you get an account and install it on your website. You can learn more about it on Google's website here.
If you already have GTM installed, then follow the instructions below to get Hello Bar installed on your site.
1) Sign into your GTM account and make sure you are signed into the right Container and then click on Add a New Tag
2) The side menu will appear and you will then need to click on the Tag Configuration top section...
3) Another side menu will appear. Scroll down until you see the Custom HTML option and click on it.