Wonderful! You have just decided that your Blogger web site needs a custom domain.
Custom domains can be added to your Blogger site, which requires domain verification through DNS settings and/or the Google Search Console.
After following all the instructions, you still have some issues with the custom domain. You may have experienced a similar message even when all the DNS settings have been entered:
You have not been authorized to use this domain. Please follow the settings instructions.
If the parking brake is still on, you are not going anywhere.
Delete the App Engine Custom Domain Mapping
Blogger may display the "not authorized" message if you have Google-managed hosting of the root domain on Google Cloud App Engine.
If you have mapped your custom domain to a Google App Engine account, then you have probably provided the usual DNS settings to make that work. Unfortunately, those same Google App Engine DNS settings will prevent Blogger from using that same domain or any other subdomains.
Deleting the App Engine domain mappings should turn off the parking brake.