DNS servers with VPN - VPN Policy-Based Routing

Hi all,

I am trying to set up my router so that all the connected devices go to internet through a VPN tunnel except for specific devices that should go through WAN.
I have installed VPN Policy-Based Routing in order to specify which IP addresses should go through WAN and everything works fine. The problem is that I need to set ISP DNS servers for the devices using WAN and VPN DNS servers for the devices using VPN.
How can I achieve that?

Thanks in advance for helping.