Hello,
Most VPN services have their desktop client applications, allowing the devices, which have them installed, to connect to VPN servers, their networks or communicate with other clients if server's configuration allows that, without any additional configuration of the router, as long as the router provides internet connectivity and the client has correct configuration, certificates. The router in this case would simply be a gateway device forwarding traffic between networks.
It would be helpful if you could provide more details on what exactly do you want to achieve.
Best regards,
