I am not an AirVPN user, but you might want to look for whether AirVPN supports filtering traffic based on port numbers, and then you can set a fixed port in your torrent client which AirVPN will always route through the VPN (and allow other traffic such as DNS and HTTPS to go around it).
Some VPNs support app-based split tunneling (such as Mullvad), but it seems from a quick search that AirVPN doesn’t. But if it supports port based filters, you can accomplish the same thing.