Welcome to the community!
The PBR app isn't needed if the user just needs to make 1 or a few rules for 1 IP:
config route
option interface 'vpn'
option target '0.0.0.0'
option netmask '0.0.0.0'
option table '2'
config rule
option src '192.168.1.xxx/32'
option dest '0.0.0.0/0'
option priority '2'
option lookup '2'
The rule can also be made for an interface instead of SRC IP - if preferred.