Forward Naked Domain
Domain Provider Redirect
If your domain provider lets you redirect your naked domain to the subdomain address (e.g. make example.com redirect to www.example.com) then configure that.
Forward Naked Domain - GoDaddy
Add an A record of @ (or your naked domain) that points to 18.104.22.168 (a free service from wwwizer.com) from https://www.steegle.com/google-sites/how-to/assign-custom-url-domain-personal