Method : 1 Meta Tag Refresh ( Recommended )
Go to Blogger Dashboard › Select a blog › Switch to Template tab › Edit HTML
Now search for <head> tag (using CTRL + F )
Copy and paste below code just below/after <head> tag
<b:if cond='data:blog.pageType == "error_page"'> Oops! Page does not exist. We are redirecting you to home page. <meta content='5;URL=http://www.your-blog-url.com' http-equiv='refresh'/> </b:if>
Finally save your template › Done.
Go to Settings › Search Preferences › Custom Page Not Found ( under Error and redirections)
Click Edit and paste below code :
Note : Change http://www.your-blog-url.com/ with your blog homepage URL and 5000 is the delay time in Milliseconds. Anyone can change it. Changing the value to Zero (0) would redirect immediately. (no delay)
Click Save Changes › Done.
Now you can test the error page code is working by entering URL that doesn’t exits in your domain. (e.g. http://your-blog-url.com/404 )