In this how-to, you’ll learn how to add a DMARC record for your domain if it’s pointed to our Basic/Premium/Free DNS.
You may also need to check:
How to add TXT/SPF/DKIM/DMARC records for a domain – https://www.namecheap.com/support/knowledgebase/article.aspx/317/2237/how-do-i-add-txtspfdkimdmarc-records-for-my-domain/
How to edit DNS zone in cPanel https://www.namecheap.com/support/knowledgebase/article.aspx/9256/29/how-to-edit-dns-zone-in-cpanel/#dmarc
What are the domain DNS options: https://www.namecheap.com/support/knowledgebase/article.aspx/10284/2254/video-what-are-the-domain-dns-options/
Find your dream domain: https://www.namecheap.com/domains/domain-name-search/