Objects > Address book > InterfaceAddresses
Add vlan500_ip, vlan500_net, vlan500_gw, vlan500_dns1, vlan500_dns2 with your values
Interfaces > Ethernet > wan
Disable option Add default route if gateway is specified
Interfaces > VLAN
Add new VLAN interface called vlan500 - over wan, VID 500, using previously created ip/new/gw objects
Rules > IP rules > lan_to_wan
Change wan to vlan500 in all rules
From this moment, you will be able to access internet via IP
Set to client PC ISP's DNS and try to use