Cloudflare: DNS → Records → Add record. Type TXT, Name _dmarc, Content the record, TTL Auto.
GoDaddy: DNS → Manage Records → Add New Record. Type TXT, Name _dmarc, Value the record.
Namecheap: Manage DNS → Add New Record. Type TXT, Host _dmarc, Value the record.
AWS Route 53: Hosted zone → Create record. Type TXT, Record name _dmarc, Value the record.
Google Workspace: DNS → Custom resource records. Type TXT, Name _dmarc, Content the record.