Step 1: Login to your Blogger Account and open your Blogger Dashboard.
Step 2: Click on settings.
Step 3: Select Basic as shown below.
Step 4: Under Publishing, go to the Blog address and click on Edit as shown above
Step 5: Go to “Advanced settings”, You will find an option saying “Redirect yourblogname.com to www.yourblogname.com” .
Step 6: Select that option and click the “Save” Button
** If you need help kindly submit a Support ticket here.