Login to your Network Solutions Account Manager.
Enter the username and password you created when you purchased your domain from Network Solutions.
From the Network Solutions Account Manager, under My Domain Names, click 'Edit DNS'.
Click 'Change Where Domain Points'.
Select 'Advanced DNS' and click 'Continue'.
Open the instructions for the type of DNS record you want to add for your domain. (TXT steps included below)
Host: Enter the host name for the TXT record. For example, enter @ for an SPF record, or enter the value _dmarc for a DMARC record.
TXT Value: The value you are setting as the destination of the Host.
TTL: Determine how long the server should cache information.
Scroll down and click 'Continue'.
Click 'Save Changes' to publish the record.
Create a free OnDMARC account to test your configuration.