If you have the HTML code, then just go into Blogger and edit your Template...

Go into Template.
Paste the code somewhere into your Template. I would suggest looking for something that says <!-- Begin #footer --> and then pasting the code right after that.

Click "Preview"... If you like it, then Save and then republish your blog.

If you don't like it, hit "Clear Edit", then paste the code somewhere else.... you can play around with it and preview a lot without hurting anything, just as long as you don't "Save" when you don't want to.