When using Google Cloud services, you can modify your domain's A records to enable your "naked" domain address. You manage A records using the administration tools at your domain host, not the Google Admin console. The exact steps for your host might vary. Below you can find generic steps that apply for any host as well as specific instructions for several popular hosts.

Don't change your domain's A records if you're using non-Google services with your domain as this will make those services unavailable. Before changing your A records, you should already be hosting your domain's website as a Google Site built in your Google account. For details, see Enable your "naked" domain address.

  1. Sign in to your domain's account at your domain host. Who is my domain host?
  2. Locate the page for updating your domain's DNS records.

    The page might be called something like DNS Management, Name Server Management, or Advanced Settings.

  3. Locate the A records for your domain. You may already have one or more records resembling:
    Name/Host/AliasTime to Live (TTL)Record TypeValue / Answer / Destination
    Blank or @86400A68.178.232.100
  4. Modify your A records so they have the A record values listed below. If necessary, create new A records to include a record for each IP address listed on this page.
    A record values

    Enter these values at your domain host, not in your Google Admin console. Note also that some hosts use different labels for the name and value fields.

    Name/Host/AliasTime to Live (TTL*)Record TypeValue/Answer/Destination
    Blank or @3600A216.239.32.21
    Blank or @3600A216.239.34.21
    Blank or @3600A216.239.36.21
    Blank or @3600A216.239.38.21

    Additionally, you may configure the following AAAA records in order to support IPv6:

    Name/Host/AliasTime to Live (TTL*)Record TypeValue/Answer/Destination
    Blank or @3600AAAA2001:4860:4802:32::15
    Blank or @3600AAAA2001:4860:4802:34::15
    Blank or @3600AAAA2001:4860:4802:36::15
    Blank or @3600AAAA2001:4860:4802:38::15

    * The TTL is the number of seconds before subsequent changes to the CNAME record go into effect. Learn more

  5. Save your changes and wait until they take effect.

A record changes can take up to 72 hours to go into effect, but typically they happen much sooner.

Need help or want to verify your change? 

To begin, see Troubleshoot A records. If you still need help after that, or if you can't access your domain's DNS records, contact your domain host directly for assistance.

Resource : https://support.google.com/a/answer/2579934?hl=en