For Pi-hole v5, you should be able to handle this by creating a custom configuration, e.g. /etc/dnsmasq.d/42-my-vlan-forwarding.conf:
rev-server=<vlan-range/CIDR>,<server.ip>
server=/<vlan.domain>/<server.ip>
where you'd substitute <vlan-range/CIDR>, <vlan.domain> and <server.ip> as required.
Afterwards, check for syntax errors:
pihole-FTL dnsmasq-test
If that returns OK:
pihole restartdns
Also, note that the upcoming Pi-hole v6 would allow you to enter those lines via its Conditional Forwarding UI, not requiring custom files anymore.