(You would use DHCP Option No. 3 - Router/Gateway.)
- The OP needs a custom route table with the VPN's gateway s the default route
- The OP will need to make a custom
ip rule
listing the IPs/IP ranges to use the VPN
The we GUI Policy Based Routing app should do this; but I never installed/used it to do so.
@moein2024,
Hope this points you in the correct direction. There are also threads you can search about the app.