OnDMARC

Log in to your <a href="http://domains.google.com/" target="_blank" rel="nofollow noopener noreferrer">Google Domains account</a>, select your 'Domain', and go to the 'DNS' section.

Scroll down to the 'Custom resource records' and create the following record:

1. Name: Enter the host name for the TXT record. For example, enter @ for an SPF record, or enter the value _dmarc for a DMARC record.
2. Type: TXT
3. Data: The value you are setting as the destination of the Host.
4. TTL: Determine how long the server should cache information.

Click 'Add' to publish the new record.

1. Log in to your <a href="http://domains.google.com/" target="_blank" rel="nofollow noopener noreferrer">Google Domains account</a>, select your 'Domain', and go to the 'DNS' section. 
2. Scroll down to the 'Custom resource records' and create the following record:
 1. Name: Enter the host name for the TXT record. For example, enter @ for an SPF record, or enter the value _dmarc for a DMARC record.
 2. Type: TXT
 3. Data: The value you are setting as the destination of the Host.
 4. TTL: Determine how long the server should cache information. 
3. Click 'Add' to publish the new record.

<a href="https://support.google.com/domains/answer/3290350?hl=en" target="_blank" rel="nofollow noopener noreferrer">Manage Resource Records with Google Domains</a> Create a free OnDMARC account to test your configuration.

How to create TXT records for SPF & DMARC with Google Domains