How to Make Robots.txt File
1.Open your Blogger Dashboard.
2.Then go to Settings then Search Preferences.
3.In Search Preferences enable custom robots.txt which will be disabled by default.
4.Enable it and paste the following code.
User-agent: Mediapartners-Google Disallow:
5.In the above code replace www.apslogo.blogspot.com with your website url then save it.
Custom Robots Header:
This is one more advanced feature provided by Blogger and must be used with proper care or else your blog might get completely deindexed from google.
1.Open blogger dashboard then Settings then choose Search Preferences.
2.Enable Custom Robots header Tags which is disabled by default and follow the below settings show in the screenshot.
Custom Robots Header for Blogger/Blogspot
1.If you are done with all the settings then save the settings to get into effect.