This post will explain the steps if you are changing from a Blogger Subdomain (blogname.blogspot.com) to a Custom Domain (customdomain.com). This is probably the easiest URL change to make in terms of steps as Blogger makes it as automatic as possible.
1. Read the first part of this post on how to smoothly change your URL or blog name, which will explain the overall steps and things to prepare before changing your URL.
2. Follow this tutorial to set up a custom domain on Blogger. Your old address (blogname.blogspot.com) will now automatically redirect to your new domain (customdomain.com) using 301 redirects so you won’t lose ranking.
3. Bloggers RSS Feed Address now will be customdomain.com/feeds/posts/default instead of blogname.blogspot.com/feeds/posts/default, this is your original feed. If you use Feedburner, the address will be the same as it was previously (feeds.feedburner.com/username) but you should login and update the original feed to customdomain.com/feeds/posts/default.
4. Your new custom domain address will still have your GFC followers and they will see new posts on their Reading List in the Blogger Dashboard. With your RSS Feed updated, you shouldn’t have a problem with Bloglovin but if you do you can contact them with your new address.