Hi guys i noticed that adding of robot.txt code has been a big challenge so i decided to drop this step by step guide to actually do this on your own without paying for anything in a very simple method.
Step 1: Login to your Blogger Dashboard
Step 2: Navigate to your Settings on the menu section
Step 3: Scroll to where you have Crawlers and Indexing
Step 4: Click on Custom Robots.txt to enable it
Step 5: Copy the code below and replace the blog url with your blog url
User-agent: *
Disallow: /search
Disallow: /category/
Disallow: /tag/
Allow: /
Sitemap: https://www.yourblogurl.blogspot.com/atom.xml?redirect=false&start-index=1&max-results=500
Step 6: Click Save and you are done.