Just to clarify, this is unrelated to OpenVPN per se as this is a pure routing problem.
You now have two different networks joint at VM1 and you want the two to be able to talk to each other.
To achieve that, you have to push a route to your VPN client with the network used to communicate to the second VM. I.e. if the connection between VM1 and VM2 uses 10.10.10.0/24 you have to add
push "route 10.10.10.0 255.255.255.0"
to your server config.
On top of that, VM2 must also have a route telling it where to find the VPN network (i.e. using VM1 as nexthop).
Lastly VM1 must have ip-forwarding enabled and the firewall should not block forwarded traffic.
I hope it helps.
