We all know, Blogger provides free lifelong SSL for blogspot domain. But Blogger also has the option to enable free SSL for the custom domain. Follow this method and enable SSL certificate on your custom domain.
Step 1: visit draft.blogger.com
Step 2: Go to section Settings >> Basic
Step 3: In the Https section, Enable Https availability.
Step 4: After, Your blogger custom domain will enable SSL soon (takes max 12 hrs)
Step 5: If you got SSL then go basic settings and enable Https redirect. This will redirect http to https.
Don’t forget to update all links on your site with https.