A DMARC record is just a TXT record for the special subdomain "_dmarc".
To add a DMARC record, do the following:
- Login to your account,
- Click on your domain name, under advanced options, click on "Modify Domain Setup",
- Here make sure the "DNS" tab is selected
- Now you can enter it on the right as shown in the screenshot:
Enter "_dmarc" as the name and the actual record as the Text data. - Click Add when everything is entered.
- Do not forget to apply the new record to the DNS settings by clicking Apply now on the left below the list of DNS records.
If you need help creating the Text Data, we can recommend this website: https://dmarcian.com/dmarc-record-wizard/