For Blogger / Blogspot blogs, you will need to do a few things. First, under settings, allow Anonymous users to comment. This is the only way your commenters will have the Name / URL option. Then, go to your Layout tab > Edit HTML. From here, you will need to Download Full Template, which will be an XML file.
Open the XML file in a text editor. Just in case there are any problems, first save a backup copy of your template. Then do a search for nofollow. You will find two lines that will simply need the rel=’nofollow’ removed from the code – one for the commenter’s URL, and one for backlinks.
<a expr:href='data:comment.authorUrl' rel='nofollow'><data:comment.author/></a>
<a expr:href='data:backlink.url' rel='nofollow'><data:backlink.title/></a>
Save your template xml, and then upload it. Now your Blogger / Blogspot should be free of nofollow links.
more info: How to Make Your WordPress or Blogger Blog DoFollow | DoFollow Blog Directory & Compendium