Yours is probably a question that should be asked of Blogspot Support.
In principle. it is just a matter of adding the code found in your Nabble forum at:
Options > Embedding options
to the page in your blog where you want it to appear.
As I am not a Blogspot user I can't help with the Blogspot specific process that will embed the forum, but it is just a matter of adding the HTML code to your blog page. What you need to do to insert HTML code within a blogspot site is definitely best asked of Blogspot Support.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.