I understand some blogging sites (e.g. Wordpress) require a paid account to be able to embed services such as Nabble's in their product, however, I believe that it should be possible with blogspot.
To insert your forum into a blogspot page, logon as an admin user and follow OPTIONS > EMBEDDING OPTIONS. That takes you to a page that will reveal the code you need to insert in your blogspot page. You'll need to turn to Blogspot's Support for information of exactly how you insert that code in their software.
To change your forum to a "Mixed" application, go to OPTIONS > EDITOR > CHANGE APPLICATION TYPE > MIXED.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.