If you want to add a new label to your existing Blogger blog post, just check screenshot below. You need to go to Posts section of Blogger admin panel. And hover your mouse on the right side of the post you want to add a label to.
Google crawler should be able to index your blog posts eventually. You don’t have to submit it. But it is recommended to submit your blogspot blog sitemap to Google Search Console. It might help you get your posts or pages indexed in Google quicker. For this, you don’t need any custom sitemap for Blogger blog. … Read more