To send custom DNS servers to clients:
Start Luci via Advanced settings.
Network->Interfaces
Find the appropriate interface, LAN for me. Click Edit.
Click to open the DHCP Server tab.
Click to open the Advanced Settings sub-tab.
In the DHCP-Options text box, enter 6 and a comma separated list of DNS server IP addresses like:
6,1.1.1.1,1.0.0.1,8.8.8.8,8.8.4.4
Click Save and then click “Unsaved changes” at the top and then click “Save and Apply”

When clients get new DHCP leases, they’ll have the list of DNS servers that you specified.

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