traffic passes through the relevant VLAN towards router 2
show:
https://openwrt.org/docs/guide-user/network/dsa/dsa-mini-tutorial#multiple_networks_using_vlan_tagging
for this I linked you how you can enable the vlans without locking yourself out of the router
alternatively if the router2 has a usb port you could connect a usb ethernet adapter and configure an administration interface ...
example:
"TP-Link UE306" - kernel module: ax88179_178a
/etc/config/network
config interface 'usblan'
option proto 'static'
option device 'eth1'
option ipaddr '192.168.50.1'
option netmask '255.255.255.0'
/etc/config/firewall
config zone
option name 'usblan'
option input 'ACCEPT'
option output 'ACCEPT'
option forward 'ACCEPT'
option masq '1'
list network 'usblan'
config forwarding
option src 'lan'
option dest 'usblan'
config forwarding
option src 'usblan'
option dest 'lan'