I use a free dmarcian account:
https://dmarcian.com/plan-free/
That website has many tools for helping you set up DMARC and checking how your DMARC, SPF, and DKIM settings are working. I’m only testing my single personal domain (low volume), so the free tool works fine for me. I use a Fastmail rule to forward the DMARC XML reports coming in from various email services to the special dmarcian address set up for my account. You can also specify that special dmarcian account address in the “rua” field of the DMARC DNS record.
Bill