You can also setup the redirect using below in the firewall file

config redirect
option name ‘Divert LAN DNS’
option src ‘lan’
option proto ‘tcpudp’
option src_dport ‘53’
option dest_port ‘53’
option target ‘DNAT’

The default rules is to drop, you can sentup the forwarding rule also

config forwarding
option src lan
option dest tun_zone