The following instructions are for setting up DoH with Brave on the desktop. The steps are similar for setting it up on Brave mobile, but if you are using Android and have blockerDNS set up as your Private DNS provider there's no need to also add it to your browser.
Go to Settings
In the Security and Privacy section go to Security
Scroll down and find the Use secure DNS option
Change the provider to Custom and then put in your custom URL: