Assuming you are only passing through one PCI device
qm set **YOUR_VM_ID** -args "-set device.hostpci0.addr=0x02"
Or manually edit your vm config from ssh or Proxomox shell:
nano /etc/pve/qemu-server/**YOUR_VM_ID**.conf
and add
-set device.hostpci0.addr=0x02
to the to the args: line line...