You would need to split ports to have different subnets. Once that is done with VPN configuration you can route your routes to subnets you want.
For example, the easiest way to do it is with ZeroTier: https://wiki.teltonika-networks.com/view/ZeroTier_Configuration
So your steps should look like this:
1. Create a new VLAN, give it ID 3, choose a port that you would like to connect a switch to, and set it to untagged (remove untagged on the ID 1 VLAN on that port).
2. Go to Interfaces and create a new interface for LAN2, choose a static protocol and use IP for a different subnet, let's say 192.168.4.1, the gateway must be the same and netmask - 255.255.255.0
3. In physical settings choose eth0.x (your created vlan interface).
4. Save everything and set-up a DHCP server then.
5. When you are done with everything above you can start configuring your ZeroTier VPN, we have enough information in our wiki.