Please read my response here why NordVPN is one of the worst choices for Bittorrent: https://forum.tixati.com/support/6946
With regards to your question, in VPN marketing speak it's called 'split tunneling.' It is up to your VPN client/VPN config to not route all
traffic via the VPN connection. As soon as that's done, you need to go to Tixati settings and set the network interface to be the VPN interface of your system (this way Tixati will ONLY bind aka use the selected interface/IP address). Tixati works wonderfully with that by the way, no hassle.
If this weren't a '****hole VPN' I'd have been inclined to help you in-depth, I just do not wish to support them in the slightest (last but not least due to history and dubious origin). Finally, there's nothing to configure in Tixati, it's all on VPN's side.